diff --git a/src/entrypoints/alpha/client.ts b/src/entrypoints/alpha/client.ts
index e619e2979..9215ba1a5 100644
--- a/src/entrypoints/alpha/client.ts
+++ b/src/entrypoints/alpha/client.ts
@@ -1,2 +1,2 @@
-export * from '../../layers/4_client/client.js'
-export { create as createSelect, select } from '../../layers/4_select/select.js'
+export * from '../../layers/5_client/client.js'
+export { create as createSelect, select } from '../../layers/5_select/select.js'
diff --git a/src/entrypoints/alpha/schema.ts b/src/entrypoints/alpha/schema.ts
index 16d24cbe4..f7b20fd98 100644
--- a/src/entrypoints/alpha/schema.ts
+++ b/src/entrypoints/alpha/schema.ts
@@ -1,3 +1,3 @@
 export * from '../../layers/1_Schema/__.js'
-export { ResultSet } from '../../layers/3_IO/ResultSet/__.js'
-export { SelectionSet } from '../../layers/3_IO/SelectionSet/__.js'
+export { SelectionSet } from '../../layers/3_SelectionSet/__.js'
+export { ResultSet } from '../../layers/4_ResultSet/__.js'
diff --git a/src/layers/3_IO/ResultSet/__.ts b/src/layers/3_IO/ResultSet/__.ts
deleted file mode 100644
index fb546c609..000000000
--- a/src/layers/3_IO/ResultSet/__.ts
+++ /dev/null
@@ -1 +0,0 @@
-export * as ResultSet from './ResultSet.js'
diff --git a/src/layers/3_IO/SelectionSet/_.ts b/src/layers/3_IO/SelectionSet/_.ts
deleted file mode 100644
index 81516ae41..000000000
--- a/src/layers/3_IO/SelectionSet/_.ts
+++ /dev/null
@@ -1,2 +0,0 @@
-export * from './SelectionSet.js'
-export * as Print from './toGraphQLDocumentString.js'
diff --git a/src/layers/3_IO/SelectionSet/toGraphQLDocumentString.ts b/src/layers/3_IO/SelectionSet/toGraphQLDocumentString.ts
deleted file mode 100644
index e23763293..000000000
--- a/src/layers/3_IO/SelectionSet/toGraphQLDocumentString.ts
+++ /dev/null
@@ -1,329 +0,0 @@
-import { RootTypeName } from '../../../lib/graphql.js'
-import { lowerCaseFirstLetter } from '../../../lib/prelude.js'
-import { Schema } from '../../1_Schema/__.js'
-import { readMaybeThunk } from '../../1_Schema/core/helpers.js'
-import type { ReturnModeType } from '../../4_client/Config.js'
-import type { SelectionSet } from './__.js'
-import { aliasPattern, fragmentPattern } from './SelectionSet.js'
-
-type SpecialFields = {
-  // todo - this requires having the schema at runtime to know which fields to select.
-  // $scalars?: SelectionSet.Indicator
-  $include?: SelectionSet.Directive.Include['$include']
-  $skip?: SelectionSet.Directive.Skip['$skip']
-  $defer?: SelectionSet.Directive.Defer['$defer']
-  $stream?: SelectionSet.Directive.Stream['$stream']
-  $?: Args
-}
-
-type Args = { [k: string]: Args_ }
-
-type Args_ = string | boolean | null | number | Args
-
-type Indicator = 0 | 1 | boolean
-
-export type DocumentObject = Record<string, GraphQLRootSelection>
-
-export type GraphQLRootSelection = { query: GraphQLObjectSelection } | { mutation: GraphQLObjectSelection }
-
-export type GraphQLObjectSelection = Record<string, Indicator | SS>
-
-export type SS = {
-  [k: string]: Indicator | SS
-} & SpecialFields
-
-export interface Context {
-  schemaIndex: Schema.Index
-  config: {
-    returnMode: ReturnModeType
-  }
-}
-
-export const rootTypeSelectionSet = (
-  context: Context,
-  schemaObject: Schema.Object$2,
-  ss: GraphQLObjectSelection,
-  name?: string,
-) => {
-  return `${lowerCaseFirstLetter(schemaObject.fields.__typename.type.type)} ${name ?? ``} { ${
-    selectionSet(context, schemaObject, ss)
-  } }`
-}
-
-const directiveArgs = (config: object) => {
-  return Object.entries(config).filter(([_, v]) => v !== undefined).map(([k, v]) => {
-    return `${k}: ${JSON.stringify(v)}`
-  }).join(`, `)
-}
-
-const resolveDirectives = (ss: Indicator | SS) => {
-  if (isIndicator(ss)) return ``
-  const { $include, $skip, $defer, $stream } = ss
-
-  let directives = ``
-
-  if ($stream !== undefined) {
-    const config = {
-      if: typeof $stream === `boolean` ? $stream : $stream.if === undefined ? true : $stream.if,
-      label: typeof $stream === `boolean` ? undefined : $stream.label,
-      initialCount: typeof $stream === `boolean` ? undefined : $stream.initialCount,
-    }
-    directives += `@stream(${directiveArgs(config)})`
-  }
-
-  if ($defer !== undefined) {
-    const config = {
-      if: typeof $defer === `boolean` ? $defer : $defer.if === undefined ? true : $defer.if,
-      label: typeof $defer === `boolean` ? undefined : $defer.label,
-    }
-    directives += `@defer(${directiveArgs(config)})`
-  }
-
-  if ($include !== undefined) {
-    directives += `@include(if: ${
-      String(typeof $include === `boolean` ? $include : $include.if === undefined ? true : $include.if)
-    })`
-  }
-
-  if ($skip !== undefined) {
-    directives += `@skip(if: ${String(typeof $skip === `boolean` ? $skip : $skip.if === undefined ? true : $skip.if)})`
-  }
-
-  return directives
-}
-
-const resolveArgs = (schemaField: Schema.SomeField, ss: Indicator | SS) => {
-  if (isIndicator(ss)) return ``
-  const { $ } = ss
-  let args = ``
-  if ($ !== undefined) {
-    const schemaArgs = schemaField.args
-    if (!schemaArgs) throw new Error(`Field has no args`)
-
-    const entries = Object.entries($)
-    args = entries.length === 0 ? `` : `(${
-      entries.map(([argName, v]) => {
-        const schemaArg = schemaArgs.fields[argName] as Schema.Input.Any | undefined // eslint-disable-line
-        if (!schemaArg) throw new Error(`Arg ${argName} not found in schema field`)
-        if (schemaArg.kind === `Enum`) {
-          return `${argName}: ${String(v)}`
-        } else {
-          // todo if enum, do not quote, requires schema index
-          return `${argName}: ${JSON.stringify(v)}`
-        }
-      }).join(`, `)
-    })`
-  }
-  return args
-}
-const pruneNonSelections = (ss: SS) => {
-  const entries = Object.entries(ss)
-  const selectEntries = entries.filter(_ => !_[0].startsWith(`$`))
-  return Object.fromEntries(selectEntries)
-}
-
-const indicatorOrSelectionSet = (
-  context: Context,
-  schemaField: Schema.SomeField,
-  ss: null | Indicator | SS,
-): string => {
-  if (ss === null) return `null` // todo test this case
-  if (isIndicator(ss)) return ``
-
-  const entries = Object.entries(ss)
-  const selectEntries = entries.filter(_ => !_[0].startsWith(`$`))
-  const directives = resolveDirectives(ss)
-  const args = resolveArgs(schemaField, ss)
-
-  if (selectEntries.length === 0) {
-    return `${args} ${directives}`
-  }
-
-  const selection = Object.fromEntries(selectEntries) as GraphQLObjectSelection
-
-  // eslint-disable-next-line
-  // @ts-ignore ID error
-  const schemaNamedOutputType = Schema.Output.unwrapToNamed(schemaField.type) as Schema.Object$2
-  return `${args} ${directives} {
-		${selectionSet(context, readMaybeThunk(schemaNamedOutputType), selection)}
-	}`
-}
-
-export const selectionSet = (
-  context: Context,
-  schemaItem: Schema.Object$2 | Schema.Union | Schema.Interface,
-  ss: Indicator | SS,
-): string => {
-  // todo optimize by doing single loop
-  const applicableSelections = Object.entries(ss).filter(([_, ss]) => isPositiveIndicator(ss)) as [
-    string,
-    SS | Indicator,
-  ][]
-  switch (schemaItem.kind) {
-    case `Object`: {
-      const rootTypeName = (RootTypeName as Record<string, RootTypeName>)[schemaItem.fields.__typename.type.type]
-        ?? null
-      return applicableSelections.map(([fieldExpression, ss]) => {
-        const fieldName = parseFieldName(fieldExpression)
-        const schemaField = schemaItem.fields[fieldName.actual]
-        if (!schemaField) throw new Error(`Field ${fieldExpression} not found in schema object`)
-        // dprint-ignore
-        if (rootTypeName&&context.config.returnMode===`successData`&&context.schemaIndex.error.rootResultFields[rootTypeName][fieldName.actual]) {
-          (ss as Record<string, boolean>)[`__typename`] = true
-        }
-        return `${resolveFragment(resolveAlias(fieldExpression))} ${indicatorOrSelectionSet(context, schemaField, ss)}`
-      }).join(`\n`) + `\n`
-    }
-    case `Interface`: {
-      return applicableSelections.map(([fieldExpression, ss]) => {
-        const fieldItem = parseFieldItem(fieldExpression)
-        switch (fieldItem._tag) {
-          case `FieldName`: {
-            if (fieldItem.actual === `__typename`) {
-              return `${renderFieldName(fieldItem)} ${resolveDirectives(ss)}`
-            }
-            const schemaField = schemaItem.fields[fieldItem.actual]
-            if (!schemaField) throw new Error(`Field ${fieldExpression} not found in schema object`)
-            // dprint-ignore
-            return `${resolveFragment(resolveAlias(fieldExpression))} ${ indicatorOrSelectionSet(context, schemaField, ss) }`
-          }
-          case `FieldOn`: {
-            const schemaObject = context.schemaIndex[`objects`][fieldItem.typeOrFragmentName]
-            if (!schemaObject) throw new Error(`Fragment ${fieldItem.typeOrFragmentName} not found in schema`)
-            return `${renderOn(fieldItem)} ${resolveDirectives(ss)} { ${selectionSet(context, schemaObject, ss)} }`
-          }
-          default: {
-            throw new Error(`Unknown field item tag`)
-          }
-        }
-      }).join(`\n`) + `\n`
-    }
-    case `Union`: {
-      return applicableSelections.map(([fieldExpression, ss]) => {
-        const fieldItem = parseFieldItem(fieldExpression)
-        switch (fieldItem._tag) {
-          case `FieldName`: {
-            if (fieldItem.actual === `__typename`) {
-              return `${renderFieldName(fieldItem)} ${resolveDirectives(ss)}`
-            }
-            // todo
-            throw new Error(`todo resolve common interface fields from unions`)
-          }
-          case `FieldOn`: {
-            const schemaObject = context.schemaIndex[`objects`][fieldItem.typeOrFragmentName]
-            if (!schemaObject) throw new Error(`Fragment ${fieldItem.typeOrFragmentName} not found in schema`)
-            // if (isIndicator(ss)) throw new Error(`Union field must have selection set`)
-            return `${renderOn(fieldItem)} ${resolveDirectives(ss)} { ${
-              // @ts-expect-error fixme
-              selectionSet(context, schemaObject, pruneNonSelections(ss))} }`
-          }
-          default: {
-            throw new Error(`Unknown field item tag`)
-          }
-        }
-      }).join(`\n`) + `\n`
-    }
-    default:
-      throw new Error(`Unknown schema item kind`)
-  }
-}
-
-type FieldItem = FieldOn | FieldName
-
-const parseFieldItem = (field: string): FieldItem => {
-  const on = parseOnExpression(field)
-  if (on) return on
-  return parseFieldName(field)
-}
-
-interface FieldOn {
-  _tag: 'FieldOn'
-  typeOrFragmentName: string
-}
-
-const parseOnExpression = (field: string): null | FieldOn => {
-  const match = field.match(fragmentPattern)
-  if (match?.groups) {
-    return {
-      _tag: `FieldOn`,
-      typeOrFragmentName: match.groups[`name`]!,
-    }
-  }
-  return null
-}
-
-const renderOn = (on: FieldOn) => {
-  return `...on ${on.typeOrFragmentName}`
-}
-
-// todo use a given schema to ensure that field is actually a fragment and not just happened to be using pattern onX
-const resolveFragment = (field: string) => {
-  const match = field.match(fragmentPattern)
-  if (match?.groups) {
-    return `...on ${match.groups[`name`]!}`
-  }
-  return field
-}
-
-interface FieldName {
-  _tag: 'FieldName'
-  actual: string
-  alias: string | null
-}
-// todo use a given schema to ensure that field is actually a fragment and not just happened to be using pattern onX
-const parseFieldName = (field: string): FieldName => {
-  const match = field.match(aliasPattern)
-  if (match?.groups) {
-    return {
-      _tag: `FieldName`,
-      actual: match.groups[`actual`]!,
-      alias: match.groups[`alias`]!,
-    }
-  }
-  return {
-    _tag: `FieldName`,
-    actual: field,
-    alias: null,
-  }
-}
-
-const renderFieldName = (fieldName: FieldName) => {
-  if (fieldName.alias) {
-    return `${fieldName.actual}: ${fieldName.alias}`
-  } else {
-    return fieldName.actual
-  }
-}
-
-// todo use a given schema to ensure that field is actually a fragment and not just happened to be using pattern onX
-const resolveAlias = (field: string) => {
-  const match = field.match(aliasPattern)
-  if (match?.groups) {
-    return `${match.groups[`actual`]!}: ${match.groups[`alias`]!}`
-  }
-  return field
-}
-
-const isIndicator = (v: any): v is Indicator => {
-  return String(v) in indicator
-}
-
-const isPositiveIndicator = (v: any): v is SelectionSet.ClientIndicatorPositive => {
-  return !(String(v) in negativeIndicator)
-}
-
-const negativeIndicator = {
-  '0': 0,
-  'false': false,
-  'undefined': undefined,
-}
-
-const positiveIndicator = {
-  '1': 1,
-  'true': true,
-}
-
-const indicator = {
-  ...negativeIndicator,
-  ...positiveIndicator,
-}
diff --git a/src/layers/3_SelectionSet/_.ts b/src/layers/3_SelectionSet/_.ts
new file mode 100644
index 000000000..4871ff9d0
--- /dev/null
+++ b/src/layers/3_SelectionSet/_.ts
@@ -0,0 +1,2 @@
+export * as Print from './encode.js'
+export * from './types.js'
diff --git a/src/layers/3_IO/SelectionSet/__.ts b/src/layers/3_SelectionSet/__.ts
similarity index 100%
rename from src/layers/3_IO/SelectionSet/__.ts
rename to src/layers/3_SelectionSet/__.ts
diff --git a/src/layers/3_IO/SelectionSet/__snapshots__/toGraphQLDocumentString.test.ts.snap b/src/layers/3_SelectionSet/__snapshots__/encode.test.ts.snap
similarity index 100%
rename from src/layers/3_IO/SelectionSet/__snapshots__/toGraphQLDocumentString.test.ts.snap
rename to src/layers/3_SelectionSet/__snapshots__/encode.test.ts.snap
diff --git a/src/layers/3_IO/SelectionSet/toGraphQLDocumentString.test.ts b/src/layers/3_SelectionSet/encode.test.ts
similarity index 94%
rename from src/layers/3_IO/SelectionSet/toGraphQLDocumentString.test.ts
rename to src/layers/3_SelectionSet/encode.test.ts
index 61d6252c5..ffabbc168 100644
--- a/src/layers/3_IO/SelectionSet/toGraphQLDocumentString.test.ts
+++ b/src/layers/3_SelectionSet/encode.test.ts
@@ -1,10 +1,10 @@
 import { parse, print } from 'graphql'
 import { describe, expect, test } from 'vitest'
-import type { Index } from '../../../../tests/_/schema/generated/Index.js'
-import { $Index as schemaIndex } from '../../../../tests/_/schema/generated/SchemaRuntime.js'
+import type { Index } from '../../../tests/_/schema/generated/Index.js'
+import { $Index as schemaIndex } from '../../../tests/_/schema/generated/SchemaRuntime.js'
 import type { SelectionSet } from './__.js'
-import type { Context } from './toGraphQLDocumentString.js'
-import { rootTypeSelectionSet } from './toGraphQLDocumentString.js'
+import type { Context } from './encode.js'
+import { rootTypeSelectionSet } from './encode.js'
 
 // eslint-disable-next-line
 // @ts-ignore
diff --git a/src/layers/3_SelectionSet/encode.ts b/src/layers/3_SelectionSet/encode.ts
new file mode 100644
index 000000000..72fbb8c12
--- /dev/null
+++ b/src/layers/3_SelectionSet/encode.ts
@@ -0,0 +1,234 @@
+import { RootTypeName } from '../../lib/graphql.js'
+import { lowerCaseFirstLetter } from '../../lib/prelude.js'
+import { Schema } from '../1_Schema/__.js'
+import { readMaybeThunk } from '../1_Schema/core/helpers.js'
+import type { ReturnModeType } from '../5_client/Config.js'
+import type { SelectionSet } from './__.js'
+import { isSelectFieldName } from './helpers.js'
+import { parseClientDirectiveDefer } from './runtime/directives/defer.js'
+import { toGraphQLDirective } from './runtime/directives/directive.js'
+import { parseClientDirectiveInclude } from './runtime/directives/include.js'
+import { parseClientDirectiveSkip } from './runtime/directives/skip.js'
+import { parseClientDirectiveStream } from './runtime/directives/stream.js'
+import { parseClientFieldItem } from './runtime/FieldItem.js'
+import { parseClientFieldName, toGraphQLFieldName } from './runtime/FieldName.js'
+import type { Indicator } from './runtime/indicator.js'
+import { isIndicator, isPositiveIndicator } from './runtime/indicator.js'
+import { parseClientOn, toGraphQLOn } from './runtime/on.js'
+
+type SpecialFields = {
+  // todo - this requires having the schema at runtime to know which fields to select.
+  // $scalars?: SelectionSet.Indicator
+  $include?: SelectionSet.Directive.Include['$include']
+  $skip?: SelectionSet.Directive.Skip['$skip']
+  $defer?: SelectionSet.Directive.Defer['$defer']
+  $stream?: SelectionSet.Directive.Stream['$stream']
+  $?: Args
+}
+
+type Args = { [k: string]: Args_ }
+
+type Args_ = string | boolean | null | number | Args
+
+export type DocumentObject = Record<string, GraphQLRootSelection>
+
+export type GraphQLRootSelection = { query: GraphQLObjectSelection } | { mutation: GraphQLObjectSelection }
+
+export type GraphQLObjectSelection = Record<string, Indicator | SS>
+
+export type SS = {
+  [k: string]: Indicator | SS
+} & SpecialFields
+
+type FieldValue = SS | Indicator
+
+export interface Context {
+  schemaIndex: Schema.Index
+  config: {
+    returnMode: ReturnModeType
+  }
+}
+
+export const rootTypeSelectionSet = (
+  context: Context,
+  schemaObject: Schema.Object$2,
+  ss: GraphQLObjectSelection,
+  operationName: string = ``,
+) => {
+  const operationTypeName = lowerCaseFirstLetter(schemaObject.fields.__typename.type.type)
+  return `${operationTypeName} ${operationName} { ${resolveObjectLikeFieldValue(context, schemaObject, ss)} }`
+}
+
+const resolveDirectives = (fieldValue: FieldValue) => {
+  if (isIndicator(fieldValue)) return ``
+
+  const { $include, $skip, $defer, $stream } = fieldValue
+
+  let directives = ``
+
+  if ($stream !== undefined) {
+    directives += toGraphQLDirective(parseClientDirectiveStream($stream))
+  }
+
+  if ($defer !== undefined) {
+    directives += toGraphQLDirective(parseClientDirectiveDefer($defer))
+  }
+
+  if ($include !== undefined) {
+    directives += toGraphQLDirective(parseClientDirectiveInclude($include))
+  }
+
+  if ($skip !== undefined) {
+    directives += toGraphQLDirective(parseClientDirectiveSkip($skip))
+  }
+
+  return directives
+}
+
+const resolveArgs = (schemaField: Schema.SomeField, ss: Indicator | SS) => {
+  if (isIndicator(ss)) return ``
+
+  const { $ } = ss
+
+  let args = ``
+  if ($ !== undefined) {
+    const schemaArgs = schemaField.args
+    if (!schemaArgs) throw new Error(`Field has no args`)
+
+    const entries = Object.entries($)
+    args = entries.length === 0 ? `` : `(${
+      entries.map(([argName, v]) => {
+        const schemaArg = schemaArgs.fields[argName] as Schema.Input.Any | undefined // eslint-disable-line
+        if (!schemaArg) throw new Error(`Arg ${argName} not found in schema field`)
+        if (schemaArg.kind === `Enum`) {
+          return `${argName}: ${String(v)}`
+        } else {
+          // todo if enum, do not quote, requires schema index
+          return `${argName}: ${JSON.stringify(v)}`
+        }
+      }).join(`, `)
+    })`
+  }
+
+  return args
+}
+const pruneNonSelections = (ss: SS) => {
+  const entries = Object.entries(ss)
+  const selectEntries = entries.filter(_ => !_[0].startsWith(`$`))
+  return Object.fromEntries(selectEntries)
+}
+
+const resolveFieldValue = (
+  context: Context,
+  schemaField: Schema.SomeField,
+  fieldValue: null | FieldValue,
+): string => {
+  if (fieldValue === null) return `null` // todo test this case
+
+  if (isIndicator(fieldValue)) return ``
+
+  const entries = Object.entries(fieldValue)
+  const directives = resolveDirectives(fieldValue)
+  const args = resolveArgs(schemaField, fieldValue)
+  const selects = entries.filter(_ => isSelectFieldName(_[0]))
+
+  if (selects.length === 0) {
+    return `${args} ${directives}`
+  }
+
+  const selection = Object.fromEntries(selects) as GraphQLObjectSelection
+
+  // eslint-disable-next-line
+  // @ts-ignore ID error
+  const schemaNamedOutputType = Schema.Output.unwrapToNamed(schemaField.type) as Schema.Object$2
+  return `${args} ${directives} {
+		${resolveObjectLikeFieldValue(context, readMaybeThunk(schemaNamedOutputType), selection)}
+	}`
+}
+
+export const resolveObjectLikeFieldValue = (
+  context: Context,
+  schemaItem: Schema.Object$2 | Schema.Union | Schema.Interface,
+  fieldValue: FieldValue,
+): string => {
+  // todo optimize by doing single loop
+  const applicableSelections = Object.entries(fieldValue).filter(([_, ss]) => isPositiveIndicator(ss)) as [
+    string,
+    FieldValue,
+  ][]
+  switch (schemaItem.kind) {
+    case `Object`: {
+      const rootTypeName = (RootTypeName as Record<string, RootTypeName>)[schemaItem.fields.__typename.type.type]
+        ?? null
+      return applicableSelections.map(([clientFieldName, ss]) => {
+        const fieldName = parseClientFieldName(clientFieldName)
+        const schemaField = schemaItem.fields[fieldName.actual]
+        if (!schemaField) throw new Error(`Field ${clientFieldName} not found in schema object`)
+        // dprint-ignore
+        if (rootTypeName && context.config.returnMode === `successData` && context.schemaIndex.error.rootResultFields[rootTypeName][fieldName.actual]) {
+          (ss as Record<string, boolean>)[`__typename`] = true
+        }
+        return `${toGraphQLFieldName(fieldName)} ${resolveFieldValue(context, schemaField, ss)}`
+      }).join(`\n`) + `\n`
+    }
+    case `Interface`: {
+      return applicableSelections.map(([ClientFieldName, ss]) => {
+        const fieldItem = parseClientFieldItem(ClientFieldName)
+
+        switch (fieldItem._tag) {
+          case `FieldName`: {
+            if (fieldItem.actual === `__typename`) {
+              return `${toGraphQLFieldName(fieldItem)} ${resolveDirectives(ss)}`
+            }
+            const schemaField = schemaItem.fields[fieldItem.actual]
+            if (!schemaField) throw new Error(`Field ${ClientFieldName} not found in schema object`)
+            return `${toGraphQLFieldName(fieldItem)} ${resolveFieldValue(context, schemaField, ss)}`
+          }
+          case `On`: {
+            const schemaObject = context.schemaIndex[`objects`][fieldItem.typeOrFragmentName]
+            if (!schemaObject) throw new Error(`Fragment ${fieldItem.typeOrFragmentName} not found in schema`)
+            return `${toGraphQLOn(fieldItem)} ${resolveDirectives(ss)} { ${
+              resolveObjectLikeFieldValue(context, schemaObject, ss)
+            } }`
+          }
+          default: {
+            throw new Error(`Unknown field item tag`)
+          }
+        }
+      }).join(`\n`) + `\n`
+    }
+    case `Union`: {
+      return applicableSelections.map(([fieldExpression, ss]) => {
+        const fieldItem = parseClientFieldItem(fieldExpression)
+        switch (fieldItem._tag) {
+          case `FieldName`: {
+            if (fieldItem.actual === `__typename`) {
+              return `${toGraphQLFieldName(fieldItem)} ${resolveDirectives(ss)}`
+            }
+            // todo
+            throw new Error(`todo resolve common interface fields from unions`)
+          }
+          case `On`: {
+            const schemaObject = context.schemaIndex[`objects`][fieldItem.typeOrFragmentName]
+            if (!schemaObject) throw new Error(`Fragment ${fieldItem.typeOrFragmentName} not found in schema`)
+            // if (isIndicator(ss)) throw new Error(`Union field must have selection set`)
+            return `${toGraphQLOn(fieldItem)} ${resolveDirectives(ss)} { ${
+              // @ts-expect-error fixme
+              resolveObjectLikeFieldValue(context, schemaObject, pruneNonSelections(ss))} }`
+          }
+          default: {
+            throw new Error(`Unknown field item tag`)
+          }
+        }
+      }).join(`\n`) + `\n`
+    }
+    default:
+      throw new Error(`Unknown schema item kind`)
+  }
+}
+
+export const resolveOn = (field: string) => {
+  const on = parseClientOn(field)
+  if (on) return toGraphQLOn(on)
+  return field
+}
diff --git a/src/layers/3_SelectionSet/helpers.ts b/src/layers/3_SelectionSet/helpers.ts
new file mode 100644
index 000000000..5d8341da3
--- /dev/null
+++ b/src/layers/3_SelectionSet/helpers.ts
@@ -0,0 +1,3 @@
+export const isSpecialFieldName = (fieldName: string) => fieldName.startsWith(`$`)
+
+export const isSelectFieldName = (fieldName: string) => !isSpecialFieldName(fieldName)
diff --git a/src/layers/3_SelectionSet/runtime/FieldItem.ts b/src/layers/3_SelectionSet/runtime/FieldItem.ts
new file mode 100644
index 000000000..af4bda18e
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/FieldItem.ts
@@ -0,0 +1,12 @@
+import type { FieldName } from './FieldName.js'
+import { parseClientFieldName } from './FieldName.js'
+import type { On } from './on.js'
+import { parseClientOn } from './on.js'
+
+export type FieldItem = On | FieldName
+
+export const parseClientFieldItem = (field: string): FieldItem => {
+  const on = parseClientOn(field)
+  if (on) return on
+  return parseClientFieldName(field)
+}
diff --git a/src/layers/3_SelectionSet/runtime/FieldName.ts b/src/layers/3_SelectionSet/runtime/FieldName.ts
new file mode 100644
index 000000000..1637063bb
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/FieldName.ts
@@ -0,0 +1,36 @@
+export interface FieldName {
+  _tag: 'FieldName'
+  actual: string
+  alias: string | null
+}
+
+// todo use a given schema to ensure that field is actually a fragment and not just happened to be using pattern onX
+export const parseClientFieldName = (field: string): FieldName => {
+  const match = field.match(aliasPattern)
+  if (match?.groups) {
+    return {
+      _tag: `FieldName`,
+      actual: match.groups[`actual`]!,
+      alias: match.groups[`alias`]!,
+    }
+  }
+  return {
+    _tag: `FieldName`,
+    actual: field,
+    alias: null,
+  }
+}
+
+export const toGraphQLFieldName = (fieldName: FieldName) => {
+  if (fieldName.alias) {
+    return `${fieldName.actual}: ${fieldName.alias}`
+  } else {
+    return fieldName.actual
+  }
+}
+
+/**
+ * @see https://regex101.com/r/XfOTMX/1
+ * @see http://spec.graphql.org/draft/#sec-Names
+ */
+export const aliasPattern = /^(?<actual>[A-z][A-z_0-9]*)_as_(?<alias>[A-z][A-z_0-9]*)$/
diff --git a/src/layers/3_SelectionSet/runtime/directives/defer.ts b/src/layers/3_SelectionSet/runtime/directives/defer.ts
new file mode 100644
index 000000000..5a5a4a55d
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/directives/defer.ts
@@ -0,0 +1,14 @@
+import type { Directive } from '../../types.js'
+
+const name = `defer`
+
+export const parseClientDirectiveDefer = (input: Directive.Defer['$defer']) => {
+  const args = {
+    if: typeof input === `boolean` ? input : input.if === undefined ? true : input.if,
+    label: typeof input === `boolean` ? undefined : input.label,
+  }
+  return {
+    name,
+    args,
+  }
+}
diff --git a/src/layers/3_SelectionSet/runtime/directives/directive.ts b/src/layers/3_SelectionSet/runtime/directives/directive.ts
new file mode 100644
index 000000000..3ff29830f
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/directives/directive.ts
@@ -0,0 +1,16 @@
+export interface DirectiveLike {
+  name: string
+  args: Record<string, any>
+}
+
+export const toGraphQLDirective = (directive: DirectiveLike) => {
+  return `@${directive.name}(${toGraphQLDirectiveArgs(directive.args)})`
+}
+
+export const toGraphQLDirectiveArgs = (args: object) => {
+  return Object.entries(args).filter(([_, v]) => v !== undefined).map(([k, clientValue]) => {
+    // todo can directives receive custom scalars?
+    const value = JSON.stringify(clientValue)
+    return `${k}: ${value}`
+  }).join(`, `)
+}
diff --git a/src/layers/3_SelectionSet/runtime/directives/include.ts b/src/layers/3_SelectionSet/runtime/directives/include.ts
new file mode 100644
index 000000000..fa7c33d24
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/directives/include.ts
@@ -0,0 +1,13 @@
+import type { Directive } from '../../types.js'
+
+const name = `include`
+
+export const parseClientDirectiveInclude = (input: Directive.Include['$include']) => {
+  const args = {
+    if: typeof input === `boolean` ? input : input.if === undefined ? true : input.if,
+  }
+  return {
+    name,
+    args,
+  }
+}
diff --git a/src/layers/3_SelectionSet/runtime/directives/skip.ts b/src/layers/3_SelectionSet/runtime/directives/skip.ts
new file mode 100644
index 000000000..a10102b61
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/directives/skip.ts
@@ -0,0 +1,13 @@
+import type { Directive } from '../../types.js'
+
+const name = `skip`
+
+export const parseClientDirectiveSkip = (input: Directive.Skip['$skip']) => {
+  const args = {
+    if: typeof input === `boolean` ? input : input.if === undefined ? true : input.if,
+  }
+  return {
+    name,
+    args,
+  }
+}
diff --git a/src/layers/3_SelectionSet/runtime/directives/stream.ts b/src/layers/3_SelectionSet/runtime/directives/stream.ts
new file mode 100644
index 000000000..84c06c448
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/directives/stream.ts
@@ -0,0 +1,15 @@
+import type { Directive } from '../../types.js'
+
+const name = `stream`
+
+export const parseClientDirectiveStream = (input: Directive.Stream['$stream']) => {
+  const args = {
+    if: typeof input === `boolean` ? input : input.if === undefined ? true : input.if,
+    label: typeof input === `boolean` ? undefined : input.label,
+    initialCount: typeof input === `boolean` ? undefined : input.initialCount,
+  }
+  return {
+    name,
+    args,
+  }
+}
diff --git a/src/layers/3_SelectionSet/runtime/indicator.ts b/src/layers/3_SelectionSet/runtime/indicator.ts
new file mode 100644
index 000000000..fe1b5a611
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/indicator.ts
@@ -0,0 +1,27 @@
+import type { ClientIndicatorPositive } from '../types.js'
+
+export type Indicator = 0 | 1 | boolean
+
+export const isIndicator = (v: any): v is Indicator => {
+  return String(v) in indicator
+}
+
+export const isPositiveIndicator = (v: any): v is ClientIndicatorPositive => {
+  return !(String(v) in negativeIndicator)
+}
+
+const negativeIndicator = {
+  '0': 0,
+  'false': false,
+  'undefined': undefined,
+}
+
+const positiveIndicator = {
+  '1': 1,
+  'true': true,
+}
+
+const indicator = {
+  ...negativeIndicator,
+  ...positiveIndicator,
+}
diff --git a/src/layers/3_SelectionSet/runtime/on.ts b/src/layers/3_SelectionSet/runtime/on.ts
new file mode 100644
index 000000000..6d1b58e39
--- /dev/null
+++ b/src/layers/3_SelectionSet/runtime/on.ts
@@ -0,0 +1,22 @@
+export const onPattern = /^on(?<name>[A-Z][A-z_0-9]*)$/
+
+export interface On {
+  _tag: 'On'
+  typeOrFragmentName: string
+}
+
+// todo use a given schema to ensure that field is actually a fragment and not just happened to be using pattern onX
+export const parseClientOn = (field: string): null | On => {
+  const match = field.match(onPattern)
+  if (match?.groups) {
+    return {
+      _tag: `On`,
+      typeOrFragmentName: match.groups[`name`]!,
+    }
+  }
+  return null
+}
+
+export const toGraphQLOn = (on: On) => {
+  return `...on ${on.typeOrFragmentName}`
+}
diff --git a/src/layers/3_IO/SelectionSet/SelectionSet.test-d.ts b/src/layers/3_SelectionSet/types.test-d.ts
similarity index 99%
rename from src/layers/3_IO/SelectionSet/SelectionSet.test-d.ts
rename to src/layers/3_SelectionSet/types.test-d.ts
index 2b46c88bf..dd670977d 100644
--- a/src/layers/3_IO/SelectionSet/SelectionSet.test-d.ts
+++ b/src/layers/3_SelectionSet/types.test-d.ts
@@ -1,5 +1,5 @@
 import { assertType, expectTypeOf, test } from 'vitest'
-import type { Index } from '../../../../tests/_/schema/generated/Index.js'
+import type { Index } from '../../../tests/_/schema/generated/Index.js'
 import type { SelectionSet } from './__.js'
 
 type Q = SelectionSet.Query<Index>
diff --git a/src/layers/3_IO/SelectionSet/SelectionSet.ts b/src/layers/3_SelectionSet/types.ts
similarity index 92%
rename from src/layers/3_IO/SelectionSet/SelectionSet.ts
rename to src/layers/3_SelectionSet/types.ts
index 37fb7f481..8546ae94a 100644
--- a/src/layers/3_IO/SelectionSet/SelectionSet.ts
+++ b/src/layers/3_SelectionSet/types.ts
@@ -1,7 +1,7 @@
 /* eslint-disable @typescript-eslint/ban-types */
 
-import type { MaybeList, StringNonEmpty, Values } from '../../../lib/prelude.js'
-import type { TSError } from '../../../lib/TSError.js'
+import type { MaybeList, StringNonEmpty, Values } from '../../lib/prelude.js'
+import type { TSError } from '../../lib/TSError.js'
 import type {
   InputFieldsAllNullable,
   OmitNullableFields,
@@ -9,7 +9,7 @@ import type {
   Schema,
   SomeField,
   SomeFields,
-} from '../../1_Schema/__.js'
+} from '../1_Schema/__.js'
 
 export type Query<$Index extends Schema.Index> = Root<$Index, 'Query'>
 
@@ -215,13 +215,6 @@ export type ClientIndicator = ClientIndicatorPositive | ClientIndicatorNegative
 export type ClientIndicatorPositive = true | 1
 export type ClientIndicatorNegative = false | 0 | undefined
 
-/**
- * @see https://regex101.com/r/XfOTMX/1
- * @see http://spec.graphql.org/draft/#sec-Names
- */
-export const aliasPattern = /^(?<actual>[A-z][A-z_0-9]*)_as_(?<alias>[A-z][A-z_0-9]*)$/
-export const fragmentPattern = /^on(?<name>[A-Z][A-z_0-9]*)$/
-
 export type OmitNegativeIndicators<$SelectionSet> = {
   [K in keyof $SelectionSet as $SelectionSet[K] extends ClientIndicatorNegative ? never : K]: $SelectionSet[K]
 }
@@ -235,10 +228,10 @@ export type NoArgsIndicator = ClientIndicator | FieldDirectives
 
 // dprint-ignore
 export type Indicator<$Field extends SomeField> =
-$Field['args'] extends Schema.Args<any>        ?  InputFieldsAllNullable<$Field['args']['fields']> extends true
-                                                    ? ({ $?: Args<$Field['args']> } & FieldDirectives) | ClientIndicator :
-                                                      { $: Args<$Field['args']> } & FieldDirectives :
-                                                  NoArgsIndicator
+  $Field['args'] extends Schema.Args<any>        ?  InputFieldsAllNullable<$Field['args']['fields']> extends true
+                                                      ? ({ $?: Args<$Field['args']> } & FieldDirectives) | ClientIndicator :
+                                                        { $: Args<$Field['args']> } & FieldDirectives :
+                                                    NoArgsIndicator
 
 // dprint-ignore
 export type Args<$Args extends Schema.Args<any>> = ArgFields<$Args['fields']>
diff --git a/src/layers/4_ResultSet/__.ts b/src/layers/4_ResultSet/__.ts
new file mode 100644
index 000000000..6ad17db77
--- /dev/null
+++ b/src/layers/4_ResultSet/__.ts
@@ -0,0 +1 @@
+export * as ResultSet from './types.js'
diff --git a/src/layers/4_ResultSet/runtime.ts b/src/layers/4_ResultSet/runtime.ts
new file mode 100644
index 000000000..045ff507a
--- /dev/null
+++ b/src/layers/4_ResultSet/runtime.ts
@@ -0,0 +1,13 @@
+import { assertObject } from '../../lib/prelude.js'
+
+// eslint-disable-next-line
+export function assertGraphQLObject(v: unknown): asserts v is GraphQLObject {
+  assertObject(v)
+  if (`__typename` in v && typeof v.__typename !== `string`) {
+    throw new Error(`Expected string __typename or undefined. Got: ${String(v.__typename)}`)
+  }
+}
+
+export type GraphQLObject = {
+  __typename?: string
+}
diff --git a/src/layers/3_IO/ResultSet/ResultSet.test-d.ts b/src/layers/4_ResultSet/types.test-d.ts
similarity index 97%
rename from src/layers/3_IO/ResultSet/ResultSet.test-d.ts
rename to src/layers/4_ResultSet/types.test-d.ts
index ad270537f..24aa76a34 100644
--- a/src/layers/3_IO/ResultSet/ResultSet.test-d.ts
+++ b/src/layers/4_ResultSet/types.test-d.ts
@@ -1,9 +1,9 @@
 /* eslint-disable @typescript-eslint/ban-types */
 
 import { expectTypeOf, test } from 'vitest'
-import type { Index } from '../../../../tests/_/schema/generated/Index.js'
-import type * as Schema from '../../../../tests/_/schema/generated/SchemaBuildtime.js'
-import type { SelectionSet } from '../SelectionSet/__.js'
+import type { Index } from '../../../tests/_/schema/generated/Index.js'
+import type * as Schema from '../../../tests/_/schema/generated/SchemaBuildtime.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
 import type { ResultSet } from './__.js'
 
 type I = Index
diff --git a/src/layers/3_IO/ResultSet/ResultSet.ts b/src/layers/4_ResultSet/types.ts
similarity index 94%
rename from src/layers/3_IO/ResultSet/ResultSet.ts
rename to src/layers/4_ResultSet/types.ts
index 9d2e59537..96a29e7f2 100644
--- a/src/layers/3_IO/ResultSet/ResultSet.ts
+++ b/src/layers/4_ResultSet/types.ts
@@ -1,11 +1,11 @@
 /* eslint-disable @typescript-eslint/ban-types */
 
 import type { Simplify } from 'type-fest'
-import type { ExcludeNull, GetKeyOr, SimplifyDeep } from '../../../lib/prelude.js'
-import type { TSError } from '../../../lib/TSError.js'
-import type { Schema, SomeField } from '../../1_Schema/__.js'
-import type { PickScalarFields } from '../../1_Schema/Output/Output.js'
-import type { SelectionSet } from '../SelectionSet/__.js'
+import type { ExcludeNull, GetKeyOr, SimplifyDeep } from '../../lib/prelude.js'
+import type { TSError } from '../../lib/TSError.js'
+import type { Schema, SomeField } from '../1_Schema/__.js'
+import type { PickScalarFields } from '../1_Schema/Output/Output.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
 
 export type Query<$SelectionSet extends object, $Index extends Schema.Index> = Root<$SelectionSet, $Index, 'Query'>
 
diff --git a/src/layers/4_client/Config.ts b/src/layers/5_client/Config.ts
similarity index 100%
rename from src/layers/4_client/Config.ts
rename to src/layers/5_client/Config.ts
diff --git a/src/layers/4_client/RootTypeMethods.ts b/src/layers/5_client/RootTypeMethods.ts
similarity index 97%
rename from src/layers/4_client/RootTypeMethods.ts
rename to src/layers/5_client/RootTypeMethods.ts
index 694d207d1..e471e25e5 100644
--- a/src/layers/4_client/RootTypeMethods.ts
+++ b/src/layers/5_client/RootTypeMethods.ts
@@ -2,8 +2,8 @@ import type { OperationName } from '../../lib/graphql.js'
 import type { Exact } from '../../lib/prelude.js'
 import type { TSError } from '../../lib/TSError.js'
 import type { InputFieldsAllNullable, Schema } from '../1_Schema/__.js'
-import type { ResultSet } from '../3_IO/ResultSet/__.js'
-import type { SelectionSet } from '../3_IO/SelectionSet/__.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
+import type { ResultSet } from '../4_ResultSet/__.js'
 import type {
   AugmentRootTypeSelectionWithTypename,
   Config,
diff --git a/src/layers/4_client/client.customScalar.test.ts b/src/layers/5_client/client.customScalar.test.ts
similarity index 100%
rename from src/layers/4_client/client.customScalar.test.ts
rename to src/layers/5_client/client.customScalar.test.ts
diff --git a/src/layers/4_client/client.document.test-d.ts b/src/layers/5_client/client.document.test-d.ts
similarity index 100%
rename from src/layers/4_client/client.document.test-d.ts
rename to src/layers/5_client/client.document.test-d.ts
diff --git a/src/layers/4_client/client.document.test.ts b/src/layers/5_client/client.document.test.ts
similarity index 100%
rename from src/layers/4_client/client.document.test.ts
rename to src/layers/5_client/client.document.test.ts
diff --git a/src/layers/4_client/client.error.test-d.ts b/src/layers/5_client/client.error.test-d.ts
similarity index 100%
rename from src/layers/4_client/client.error.test-d.ts
rename to src/layers/5_client/client.error.test-d.ts
diff --git a/src/layers/4_client/client.input.test-d.ts b/src/layers/5_client/client.input.test-d.ts
similarity index 100%
rename from src/layers/4_client/client.input.test-d.ts
rename to src/layers/5_client/client.input.test-d.ts
diff --git a/src/layers/4_client/client.returnMode.test-d.ts b/src/layers/5_client/client.returnMode.test-d.ts
similarity index 100%
rename from src/layers/4_client/client.returnMode.test-d.ts
rename to src/layers/5_client/client.returnMode.test-d.ts
diff --git a/src/layers/4_client/client.returnMode.test.ts b/src/layers/5_client/client.returnMode.test.ts
similarity index 100%
rename from src/layers/4_client/client.returnMode.test.ts
rename to src/layers/5_client/client.returnMode.test.ts
diff --git a/src/layers/4_client/client.rootTypeMethods.test-d.ts b/src/layers/5_client/client.rootTypeMethods.test-d.ts
similarity index 100%
rename from src/layers/4_client/client.rootTypeMethods.test-d.ts
rename to src/layers/5_client/client.rootTypeMethods.test-d.ts
diff --git a/src/layers/4_client/client.rootTypeMethods.test.ts b/src/layers/5_client/client.rootTypeMethods.test.ts
similarity index 100%
rename from src/layers/4_client/client.rootTypeMethods.test.ts
rename to src/layers/5_client/client.rootTypeMethods.test.ts
diff --git a/src/layers/4_client/client.ts b/src/layers/5_client/client.ts
similarity index 98%
rename from src/layers/4_client/client.ts
rename to src/layers/5_client/client.ts
index 893a68510..3e5fa8eae 100644
--- a/src/layers/4_client/client.ts
+++ b/src/layers/5_client/client.ts
@@ -3,14 +3,14 @@ import { type DocumentNode, execute, graphql, type GraphQLSchema } from 'graphql
 import type { ExcludeUndefined } from 'type-fest/source/required-deep.js'
 import request from '../../entrypoints/main.js'
 import { Errors } from '../../lib/errors/__.js'
-import type { RootTypeName, Variables } from '../../lib/graphql.js'
+import { type RootTypeName, rootTypeNameToOperationName, type Variables } from '../../lib/graphql.js'
 import { isPlainObject } from '../../lib/prelude.js'
 import type { Object$2 } from '../1_Schema/__.js'
 import { Schema } from '../1_Schema/__.js'
 import { readMaybeThunk } from '../1_Schema/core/helpers.js'
 import type { GlobalRegistry } from '../2_generator/globalRegistry.js'
-import { SelectionSet } from '../3_IO/SelectionSet/__.js'
-import type { Context, DocumentObject, GraphQLObjectSelection } from '../3_IO/SelectionSet/toGraphQLDocumentString.js'
+import { SelectionSet } from '../3_SelectionSet/__.js'
+import type { Context, DocumentObject, GraphQLObjectSelection } from '../3_SelectionSet/encode.js'
 import type {
   ApplyInputDefaults,
   Config,
@@ -20,7 +20,7 @@ import type {
 } from './Config.js'
 import * as CustomScalars from './customScalars.js'
 import type { DocumentFn } from './document.js'
-import { rootTypeNameToOperationName, toDocumentString } from './document.js'
+import { toDocumentString } from './document.js'
 import type { GetRootTypeMethods } from './RootTypeMethods.js'
 
 // dprint-ignore
diff --git a/src/layers/4_client/customScalars.ts b/src/layers/5_client/customScalars.ts
similarity index 85%
rename from src/layers/4_client/customScalars.ts
rename to src/layers/5_client/customScalars.ts
index af306ed14..e90b7e4ee 100644
--- a/src/layers/4_client/customScalars.ts
+++ b/src/layers/5_client/customScalars.ts
@@ -1,12 +1,14 @@
 import type { ExecutionResult } from 'graphql'
 import { standardScalarTypeNames } from '../../lib/graphql.js'
-import { mapValues } from '../../lib/prelude.js'
+import { assertArray, mapValues } from '../../lib/prelude.js'
 import type { Object$2, Schema } from '../1_Schema/__.js'
 import { Output } from '../1_Schema/__.js'
 import { readMaybeThunk } from '../1_Schema/core/helpers.js'
-import type { SelectionSet } from '../3_IO/SelectionSet/__.js'
-import type { Args } from '../3_IO/SelectionSet/SelectionSet.js'
-import type { GraphQLObjectSelection } from '../3_IO/SelectionSet/toGraphQLDocumentString.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
+import type { GraphQLObjectSelection } from '../3_SelectionSet/encode.js'
+import type { Args } from '../3_SelectionSet/types.js'
+import type { GraphQLObject } from '../4_ResultSet/runtime.js'
+import { assertGraphQLObject } from '../4_ResultSet/runtime.js'
 
 namespace SSValue {
   export type Obj = {
@@ -149,25 +151,3 @@ const decodeCustomScalarValue = (
 
   return fieldValue
 }
-
-// eslint-disable-next-line
-function assertArray(v: unknown): asserts v is unknown[] {
-  if (!Array.isArray(v)) throw new Error(`Expected array. Got: ${String(v)}`)
-}
-
-// eslint-disable-next-line
-function assertObject(v: unknown): asserts v is object {
-  if (v === null || typeof v !== `object`) throw new Error(`Expected object. Got: ${String(v)}`)
-}
-
-// eslint-disable-next-line
-function assertGraphQLObject(v: unknown): asserts v is GraphQLObject {
-  assertObject(v)
-  if (`__typename` in v && typeof v.__typename !== `string`) {
-    throw new Error(`Expected string __typename or undefined. Got: ${String(v.__typename)}`)
-  }
-}
-
-type GraphQLObject = {
-  __typename?: string
-}
diff --git a/src/layers/4_client/document.ts b/src/layers/5_client/document.ts
similarity index 90%
rename from src/layers/4_client/document.ts
rename to src/layers/5_client/document.ts
index cd627f5ce..fc55b3806 100644
--- a/src/layers/4_client/document.ts
+++ b/src/layers/5_client/document.ts
@@ -1,10 +1,11 @@
 import type { MergeExclusive, NonEmptyObject } from 'type-fest'
+import { operationTypeToRootType } from '../../lib/graphql.js'
 import type { IsMultipleKeys } from '../../lib/prelude.js'
 import type { TSError } from '../../lib/TSError.js'
 import type { Schema } from '../1_Schema/__.js'
-import type { ResultSet } from '../3_IO/ResultSet/__.js'
-import { SelectionSet } from '../3_IO/SelectionSet/__.js'
-import type { Context, DocumentObject } from '../3_IO/SelectionSet/toGraphQLDocumentString.js'
+import { SelectionSet } from '../3_SelectionSet/__.js'
+import type { Context, DocumentObject } from '../3_SelectionSet/encode.js'
+import type { ResultSet } from '../4_ResultSet/__.js'
 import type { AugmentRootTypeSelectionWithTypename, Config, OrThrowifyConfig, ReturnModeRootType } from './Config.js'
 
 // dprint-ignore
@@ -91,15 +92,3 @@ type GetRootType<$Selection extends object> =
   $Selection extends {query:any}    ? 'Query' : 
   $Selection extends {mutation:any} ? 'Mutation' :
   never
-
-export const operationTypeToRootType = {
-  query: `Query`,
-  mutation: `Mutation`,
-  subscription: `Subscription`,
-} as const
-
-export const rootTypeNameToOperationName = {
-  Query: `query`,
-  Mutation: `mutation`,
-  Subscription: `subscription`,
-} as const
diff --git a/src/layers/4_select/select.test-d.ts b/src/layers/5_select/select.test-d.ts
similarity index 94%
rename from src/layers/4_select/select.test-d.ts
rename to src/layers/5_select/select.test-d.ts
index 348ba65fe..d15d2a5c0 100644
--- a/src/layers/4_select/select.test-d.ts
+++ b/src/layers/5_select/select.test-d.ts
@@ -1,7 +1,7 @@
 import { describe, expect, expectTypeOf, it, test } from 'vitest'
 import type { Index } from '../../../tests/_/schema/schema.js'
 import type * as SchemaQueryOnly from '../../../tests/_/schemaQueryOnly/generated/Index.js'
-import type { SelectionSet } from '../3_IO/SelectionSet/__.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
 import { create } from './select.js'
 
 describe(`select`, () => {
diff --git a/src/layers/4_select/select.test.ts b/src/layers/5_select/select.test.ts
similarity index 100%
rename from src/layers/4_select/select.test.ts
rename to src/layers/5_select/select.test.ts
diff --git a/src/layers/4_select/select.ts b/src/layers/5_select/select.ts
similarity index 95%
rename from src/layers/4_select/select.ts
rename to src/layers/5_select/select.ts
index eb5108649..90629db1f 100644
--- a/src/layers/4_select/select.ts
+++ b/src/layers/5_select/select.ts
@@ -1,7 +1,7 @@
 import type { RootTypeName } from '../../lib/graphql.js'
 import type { Exact } from '../../lib/prelude.js'
 import type { Schema } from '../1_Schema/__.js'
-import type { SelectionSet } from '../3_IO/SelectionSet/__.js'
+import type { SelectionSet } from '../3_SelectionSet/__.js'
 
 // dprint-ignore
 type TypeSelectionSets<$Index extends Schema.Index> =
diff --git a/src/lib/graphql.ts b/src/lib/graphql.ts
index d3fd2dd33..166b46120 100644
--- a/src/lib/graphql.ts
+++ b/src/lib/graphql.ts
@@ -35,6 +35,18 @@ export const RootTypeName = {
   Subscription: `Subscription`,
 } as const
 
+export const operationTypeToRootType = {
+  query: `Query`,
+  mutation: `Mutation`,
+  subscription: `Subscription`,
+} as const
+
+export const rootTypeNameToOperationName = {
+  Query: `query`,
+  Mutation: `mutation`,
+  Subscription: `subscription`,
+} as const
+
 export type RootTypeName = keyof typeof RootTypeName
 
 export const isStandardScalarType = (type: GraphQLScalarType) => {
diff --git a/src/lib/prelude.ts b/src/lib/prelude.ts
index 1ae0337cf..8a33c4619 100644
--- a/src/lib/prelude.ts
+++ b/src/lib/prelude.ts
@@ -237,3 +237,11 @@ export type SetProperty<$Obj extends object, $Prop extends keyof $Obj, $Type ext
 export const lowerCaseFirstLetter = (s: string) => {
   return s.charAt(0).toLowerCase() + s.slice(1)
 }
+
+export function assertArray(v: unknown): asserts v is unknown[] {
+  if (!Array.isArray(v)) throw new Error(`Expected array. Got: ${String(v)}`)
+}
+
+export function assertObject(v: unknown): asserts v is object {
+  if (v === null || typeof v !== `object`) throw new Error(`Expected object. Got: ${String(v)}`)
+}