diff --git a/parser_library/src/expressions/conditional_assembly/ca_expression.h b/parser_library/src/expressions/conditional_assembly/ca_expression.h
index 6e9f93a49..4174985ff 100644
--- a/parser_library/src/expressions/conditional_assembly/ca_expression.h
+++ b/parser_library/src/expressions/conditional_assembly/ca_expression.h
@@ -27,7 +27,6 @@ namespace hlasm_plugin::parser_library::expressions {
 class ca_expr_visitor;
 class ca_expression;
 using ca_expr_ptr = std::unique_ptr<ca_expression>;
-using undef_sym_set = std::set<context::id_index>;
 
 struct evaluation_context;
 
@@ -60,7 +59,8 @@ class ca_expression
     ca_expression(context::SET_t_enum expr_kind, range expr_range);
 
     // retrieves set of attributed symbols that are not yet defined
-    virtual bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const = 0;
+    virtual bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const = 0;
 
     // builds parts of the expression tree that could not be built during parsing
     virtual void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) = 0;
diff --git a/parser_library/src/expressions/conditional_assembly/ca_operator_binary.cpp b/parser_library/src/expressions/conditional_assembly/ca_operator_binary.cpp
index 9942317e7..99834702d 100644
--- a/parser_library/src/expressions/conditional_assembly/ca_operator_binary.cpp
+++ b/parser_library/src/expressions/conditional_assembly/ca_operator_binary.cpp
@@ -34,7 +34,7 @@ ca_binary_operator::ca_binary_operator(
 {}
 
 bool ca_binary_operator::get_undefined_attributed_symbols(
-    undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     bool result = false;
     result |= left_expr->get_undefined_attributed_symbols(symbols, eval_ctx);
@@ -79,7 +79,7 @@ ca_function_binary_operator::ca_function_binary_operator(ca_expr_ptr left_expr,
 {}
 
 // Detects (T'&VAR EQ 'O') condition
-std::optional<bool> t_attr_special_case(undef_sym_set& symbols,
+std::optional<bool> t_attr_special_case(std::vector<context::id_index>& symbols,
     const expressions::ca_expression* left,
     const expressions::ca_expression* right,
     const evaluation_context& eval_ctx)
@@ -116,7 +116,7 @@ std::optional<bool> t_attr_special_case(undef_sym_set& symbols,
 }
 
 bool ca_function_binary_operator::get_undefined_attributed_symbols(
-    undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     if (is_relational() && m_expr_ctx.parent_expr_kind == context::SET_t_enum::B_TYPE)
     {
diff --git a/parser_library/src/expressions/conditional_assembly/ca_operator_binary.h b/parser_library/src/expressions/conditional_assembly/ca_operator_binary.h
index 9e0759fac..3bc5a3f39 100644
--- a/parser_library/src/expressions/conditional_assembly/ca_operator_binary.h
+++ b/parser_library/src/expressions/conditional_assembly/ca_operator_binary.h
@@ -29,7 +29,8 @@ class ca_binary_operator : public ca_expression
 
     ca_binary_operator(ca_expr_ptr left_expr, ca_expr_ptr right_expr, context::SET_t_enum expr_kind, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
@@ -69,7 +70,8 @@ class ca_function_binary_operator final : public ca_binary_operator
         range expr_range,
         context::SET_t_enum parent_expr_kind = context::SET_t_enum::UNDEF_TYPE);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/ca_operator_unary.cpp b/parser_library/src/expressions/conditional_assembly/ca_operator_unary.cpp
index 5884669cb..d1d25a855 100644
--- a/parser_library/src/expressions/conditional_assembly/ca_operator_unary.cpp
+++ b/parser_library/src/expressions/conditional_assembly/ca_operator_unary.cpp
@@ -28,7 +28,7 @@ ca_unary_operator::ca_unary_operator(ca_expr_ptr expr, context::SET_t_enum expr_
 {}
 
 bool ca_unary_operator::get_undefined_attributed_symbols(
-    undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     return expr->get_undefined_attributed_symbols(symbols, eval_ctx);
 }
diff --git a/parser_library/src/expressions/conditional_assembly/ca_operator_unary.h b/parser_library/src/expressions/conditional_assembly/ca_operator_unary.h
index 5ea24bf5e..53e422de0 100644
--- a/parser_library/src/expressions/conditional_assembly/ca_operator_unary.h
+++ b/parser_library/src/expressions/conditional_assembly/ca_operator_unary.h
@@ -27,7 +27,8 @@ class ca_unary_operator : public ca_expression
 
     ca_unary_operator(ca_expr_ptr expr, context::SET_t_enum expr_kind, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_constant.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_constant.cpp
index 953d68e20..a155685c4 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_constant.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_constant.cpp
@@ -26,7 +26,10 @@ ca_constant::ca_constant(context::A_t value, range expr_range)
     , value(value)
 {}
 
-bool ca_constant::get_undefined_attributed_symbols(undef_sym_set&, const evaluation_context&) const { return false; }
+bool ca_constant::get_undefined_attributed_symbols(std::vector<context::id_index>&, const evaluation_context&) const
+{
+    return false;
+}
 
 void ca_constant::resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags)
 {
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_constant.h b/parser_library/src/expressions/conditional_assembly/terms/ca_constant.h
index 3fc98327f..10fce2955 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_constant.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_constant.h
@@ -31,7 +31,8 @@ class ca_constant final : public ca_expression
 
     ca_constant(context::A_t value, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.cpp
index 3bb085c4f..edc3d412a 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.cpp
@@ -31,7 +31,8 @@ ca_expr_list::ca_expr_list(std::vector<ca_expr_ptr> expr_list, range expr_range,
     , parenthesized(parenthesized)
 {}
 
-bool ca_expr_list::get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+bool ca_expr_list::get_undefined_attributed_symbols(
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     bool result = false;
     for (auto&& expr : expr_list)
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.h b/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.h
index b0568e706..973c8461f 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_expr_list.h
@@ -28,7 +28,8 @@ class ca_expr_list final : public ca_expression
 public:
     ca_expr_list(std::vector<ca_expr_ptr> expr_list, range expr_range, bool parenthesized);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_function.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_function.cpp
index a549b7a12..08b450622 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_function.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_function.cpp
@@ -48,7 +48,8 @@ ca_function::ca_function(context::id_index function_name,
     , duplication_factor(std::move(duplication_factor))
 {}
 
-bool ca_function::get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+bool ca_function::get_undefined_attributed_symbols(
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     bool result = false;
     for (auto&& expr : parameters)
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_function.h b/parser_library/src/expressions/conditional_assembly/terms/ca_function.h
index 49e228240..0d0c7e1bc 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_function.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_function.h
@@ -40,7 +40,8 @@ class ca_function final : public ca_expression
         ca_expr_ptr duplication_factor,
         range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_string.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_string.cpp
index 2260f3d6b..ff6bec089 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_string.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_string.cpp
@@ -38,7 +38,8 @@ ca_string::ca_string(
     , substring(std::move(substring))
 {}
 
-bool ca_string::get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+bool ca_string::get_undefined_attributed_symbols(
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     bool result = false;
     if (duplication_factor)
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_string.h b/parser_library/src/expressions/conditional_assembly/terms/ca_string.h
index a2c473a38..c3e4c2562 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_string.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_string.h
@@ -39,7 +39,8 @@ class ca_string final : public ca_expression
 
     ca_string(semantics::concat_chain value, ca_expr_ptr duplication_factor, substring_t substring, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.cpp
index 6f900883e..7d1117602 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.cpp
@@ -25,7 +25,10 @@ ca_symbol::ca_symbol(context::id_index symbol, range expr_range)
     , symbol(symbol)
 {}
 
-bool ca_symbol::get_undefined_attributed_symbols(undef_sym_set&, const evaluation_context&) const { return false; }
+bool ca_symbol::get_undefined_attributed_symbols(std::vector<context::id_index>&, const evaluation_context&) const
+{
+    return false;
+}
 
 void ca_symbol::resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags)
 {
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.h b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.h
index 26c8bc69e..73f23fac4 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol.h
@@ -27,7 +27,8 @@ class ca_symbol final : public ca_expression
 
     ca_symbol(context::id_index symbol, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.cpp
index e511f102d..ffc33fe80 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.cpp
@@ -18,14 +18,12 @@
 #include "ca_var_sym.h"
 #include "context/hlasm_context.h"
 #include "context/literal_pool.h"
-#include "context/ordinary_assembly/dependable.h"
 #include "context/ordinary_assembly/ordinary_assembly_dependency_solver.h"
 #include "diagnostic_consumer.h"
 #include "ebcdic_encoding.h"
 #include "expressions/conditional_assembly/ca_expr_visitor.h"
 #include "expressions/evaluation_context.h"
 #include "lexing/lexer.h"
-#include "lexing/token_stream.h"
 #include "parsing/parser_impl.h"
 #include "processing/op_code.h"
 #include "semantics/range_provider.h"
@@ -78,7 +76,7 @@ ca_symbol_attribute::ca_symbol_attribute(
 {}
 
 bool ca_symbol_attribute::get_undefined_attributed_symbols(
-    undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     if (std::holds_alternative<context::id_index>(symbol))
     {
@@ -86,7 +84,7 @@ bool ca_symbol_attribute::get_undefined_attributed_symbols(
             && !eval_ctx.hlasm_ctx.ord_ctx.get_symbol(std::get<context::id_index>(symbol))
             && !eval_ctx.hlasm_ctx.ord_ctx.get_symbol_reference(std::get<context::id_index>(symbol)))
         {
-            symbols.emplace(std::get<context::id_index>(symbol));
+            symbols.emplace_back(std::get<context::id_index>(symbol));
             return true;
         }
     }
@@ -113,7 +111,7 @@ bool ca_symbol_attribute::get_undefined_attributed_symbols(
                 && !eval_ctx.hlasm_ctx.ord_ctx.get_symbol(ord_name)
                 && !eval_ctx.hlasm_ctx.ord_ctx.get_symbol_reference(ord_name))
             {
-                symbols.emplace(ord_name);
+                symbols.emplace_back(ord_name);
                 return true;
             }
         }
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.h b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.h
index 76964759a..f87f7954e 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_symbol_attribute.h
@@ -42,7 +42,8 @@ class ca_symbol_attribute final : public ca_expression
     ca_symbol_attribute(
         semantics::literal_si lit, context::data_attr_kind attribute, range expr_range, range symbol_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.cpp b/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.cpp
index d3e88efa9..0f338a09e 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.cpp
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.cpp
@@ -27,7 +27,7 @@ ca_var_sym::ca_var_sym(semantics::vs_ptr symbol, range expr_range)
 {}
 
 bool ca_var_sym::get_undefined_attributed_symbols_vs(
-    undef_sym_set& symbols, const semantics::vs_ptr& symbol, const evaluation_context& eval_ctx)
+    std::vector<context::id_index>& symbols, const semantics::vs_ptr& symbol, const evaluation_context& eval_ctx)
 {
     bool result = false;
 
@@ -44,7 +44,8 @@ bool ca_var_sym::get_undefined_attributed_symbols_vs(
     return result;
 }
 
-bool ca_var_sym::get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const
+bool ca_var_sym::get_undefined_attributed_symbols(
+    std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const
 {
     return get_undefined_attributed_symbols_vs(symbols, symbol, eval_ctx);
 }
diff --git a/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.h b/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.h
index 03b2d9ca1..519918ddf 100644
--- a/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.h
+++ b/parser_library/src/expressions/conditional_assembly/terms/ca_var_sym.h
@@ -28,7 +28,8 @@ class ca_var_sym final : public ca_expression
 
     ca_var_sym(semantics::vs_ptr symbol, range expr_range);
 
-    bool get_undefined_attributed_symbols(undef_sym_set& symbols, const evaluation_context& eval_ctx) const override;
+    bool get_undefined_attributed_symbols(
+        std::vector<context::id_index>& symbols, const evaluation_context& eval_ctx) const override;
 
     void resolve_expression_tree(ca_expression_ctx expr_ctx, diagnostic_op_consumer& diags) override;
 
@@ -39,7 +40,7 @@ class ca_var_sym final : public ca_expression
     context::SET_t evaluate(const evaluation_context& eval_ctx) const override;
 
     static bool get_undefined_attributed_symbols_vs(
-        undef_sym_set& symbols, const semantics::vs_ptr& symbol, const evaluation_context& eval_ctx);
+        std::vector<context::id_index>& symbols, const semantics::vs_ptr& symbol, const evaluation_context& eval_ctx);
 
 private:
     context::SET_t convert_return_types(
diff --git a/parser_library/src/processing/opencode_provider.cpp b/parser_library/src/processing/opencode_provider.cpp
index 7f9b5d7da..50e1d7ab7 100644
--- a/parser_library/src/processing/opencode_provider.cpp
+++ b/parser_library/src/processing/opencode_provider.cpp
@@ -477,7 +477,8 @@ std::shared_ptr<const context::hlasm_statement> opencode_provider::process_ordin
     if (proc.kind == processing_kind::ORDINARY
         && try_trigger_attribute_lookahead(*result,
             { *m_ctx->hlasm_ctx, library_info_transitional(*m_lib_provider), drop_diagnostic_op },
-            *m_state_listener))
+            *m_state_listener,
+            std::move(lookahead_references)))
         return nullptr;
 
     if (m_current_logical_line.segments.size() > 1)
@@ -725,7 +726,8 @@ context::shared_stmt_ptr opencode_provider::get_next(const statement_processor&
     if (proc.kind == processing_kind::ORDINARY
         && try_trigger_attribute_lookahead(collector.current_instruction(),
             { *m_ctx->hlasm_ctx, library_info_transitional(*m_lib_provider), drop_diagnostic_op },
-            *m_state_listener))
+            *m_state_listener,
+            std::move(lookahead_references)))
         return nullptr;
 
     const auto& current_instr = collector.current_instruction();
diff --git a/parser_library/src/processing/opencode_provider.h b/parser_library/src/processing/opencode_provider.h
index 3c2b72572..5a8c5589a 100644
--- a/parser_library/src/processing/opencode_provider.h
+++ b/parser_library/src/processing/opencode_provider.h
@@ -163,6 +163,8 @@ class opencode_provider final : public statement_provider
 
     encoding_warning_issued m_encoding_warning_issued = {};
 
+    std::vector<context::id_index> lookahead_references;
+
 public:
     // rewinds position in file
     void rewind_input(context::source_position pos);
diff --git a/parser_library/src/processing/statement_processors/lookahead_processing_info.h b/parser_library/src/processing/statement_processors/lookahead_processing_info.h
index 5cf480fdd..7206ff5b7 100644
--- a/parser_library/src/processing/statement_processors/lookahead_processing_info.h
+++ b/parser_library/src/processing/statement_processors/lookahead_processing_info.h
@@ -15,7 +15,7 @@
 #ifndef PROCESSING_LOOKAHEAD_PROCESSING_INFO_H
 #define PROCESSING_LOOKAHEAD_PROCESSING_INFO_H
 
-#include <set>
+#include <vector>
 
 #include "context/ordinary_assembly/symbol.h"
 #include "context/source_snapshot.h"
@@ -51,9 +51,9 @@ struct lookahead_start_data
     {}
 
     // ORD action
-    std::set<context::id_index> targets;
+    std::vector<context::id_index> targets;
 
-    lookahead_start_data(std::set<context::id_index> targets,
+    lookahead_start_data(std::vector<context::id_index> targets,
         context::source_position statement_position,
         context::source_snapshot snapshot)
         : action(lookahead_action::ORD)
diff --git a/parser_library/src/processing/statement_processors/lookahead_processor.cpp b/parser_library/src/processing/statement_processors/lookahead_processor.cpp
index 2867dfd24..52154d28e 100644
--- a/parser_library/src/processing/statement_processors/lookahead_processor.cpp
+++ b/parser_library/src/processing/statement_processors/lookahead_processor.cpp
@@ -324,7 +324,11 @@ void lookahead_processor::find_ord(const resolved_statement& statement)
     if (!valid)
         return;
 
-    to_find_.erase(id);
+    if (auto it = std::find(to_find_.begin(), to_find_.end(), id); it != to_find_.end())
+    {
+        std::swap(*it, to_find_.back());
+        to_find_.pop_back();
+    }
 
     // find attributes
     // if found ord symbol on CA, macro or undefined instruction, only type attribute is assigned
diff --git a/parser_library/src/processing/statement_processors/lookahead_processor.h b/parser_library/src/processing/statement_processors/lookahead_processor.h
index 58b5c5d72..dc9e7fff2 100644
--- a/parser_library/src/processing/statement_processors/lookahead_processor.h
+++ b/parser_library/src/processing/statement_processors/lookahead_processor.h
@@ -36,7 +36,7 @@ class lookahead_processor final : public statement_processor
     processing_state_listener& listener_;
     workspaces::parse_lib_provider& lib_provider_;
 
-    std::set<context::id_index> to_find_;
+    std::vector<context::id_index> to_find_;
     context::id_index target_;
 
 public:
diff --git a/parser_library/src/processing/statement_providers/members_statement_provider.cpp b/parser_library/src/processing/statement_providers/members_statement_provider.cpp
index e9787dd7c..0b46a2693 100644
--- a/parser_library/src/processing/statement_providers/members_statement_provider.cpp
+++ b/parser_library/src/processing/statement_providers/members_statement_provider.cpp
@@ -48,7 +48,8 @@ context::shared_stmt_ptr members_statement_provider::get_next(const statement_pr
         {
             if (try_trigger_attribute_lookahead(*instr,
                     { *m_ctx.hlasm_ctx, library_info_transitional(m_lib_provider), drop_diagnostic_op },
-                    m_listener))
+                    m_listener,
+                    std::move(lookahead_references)))
                 return nullptr;
         }
     }
@@ -83,8 +84,10 @@ context::shared_stmt_ptr members_statement_provider::get_next(const statement_pr
     }
 
     if (processor.kind == processing_kind::ORDINARY
-        && try_trigger_attribute_lookahead(
-            *stmt, { *m_ctx.hlasm_ctx, library_info_transitional(m_lib_provider), drop_diagnostic_op }, m_listener))
+        && try_trigger_attribute_lookahead(*stmt,
+            { *m_ctx.hlasm_ctx, library_info_transitional(m_lib_provider), drop_diagnostic_op },
+            m_listener,
+            std::move(lookahead_references)))
         return nullptr;
 
     return stmt;
diff --git a/parser_library/src/processing/statement_providers/members_statement_provider.h b/parser_library/src/processing/statement_providers/members_statement_provider.h
index f39e2ff6c..d4e66fae0 100644
--- a/parser_library/src/processing/statement_providers/members_statement_provider.h
+++ b/parser_library/src/processing/statement_providers/members_statement_provider.h
@@ -37,6 +37,8 @@ namespace hlasm_plugin::parser_library::processing {
 // common class for copy and macro statement providers (provider of copy and macro members)
 class members_statement_provider : public statement_provider
 {
+    std::vector<context::id_index> lookahead_references;
+
 public:
     members_statement_provider(const statement_provider_kind kind,
         analyzing_context ctx,
diff --git a/parser_library/src/processing/statement_providers/statement_provider.cpp b/parser_library/src/processing/statement_providers/statement_provider.cpp
index 93ac7f92f..1a6ff9a45 100644
--- a/parser_library/src/processing/statement_providers/statement_provider.cpp
+++ b/parser_library/src/processing/statement_providers/statement_provider.cpp
@@ -26,25 +26,27 @@ statement_provider::statement_provider(const statement_provider_kind kind)
 
 bool statement_provider::try_trigger_attribute_lookahead(const semantics::instruction_si& instruction,
     expressions::evaluation_context eval_ctx,
-    processing::processing_state_listener& listener)
+    processing::processing_state_listener& listener,
+    std::vector<context::id_index>&& references_buffer)
 {
-    std::set<context::id_index> references;
-    process_instruction(references, instruction, eval_ctx);
+    references_buffer.clear();
+    process_instruction(references_buffer, instruction, eval_ctx);
 
-    if (references.empty())
+    if (references_buffer.empty())
         return false;
 
-    trigger_attribute_lookahead(std::move(references), eval_ctx, listener);
+    trigger_attribute_lookahead(std::move(references_buffer), eval_ctx, listener);
 
     return true;
 }
 
 bool statement_provider::try_trigger_attribute_lookahead(const context::hlasm_statement& statement,
     expressions::evaluation_context eval_ctx,
-    processing::processing_state_listener& listener)
+    processing::processing_state_listener& listener,
+    std::vector<context::id_index>&& references_buffer)
 {
+    references_buffer.clear();
     const semantics::label_si* label;
-    std::set<context::id_index> references;
 
     if (auto def_stmt = statement.access_deferred())
     {
@@ -54,31 +56,36 @@ bool statement_provider::try_trigger_attribute_lookahead(const context::hlasm_st
     {
         label = &res_stmt->label_ref();
 
-        process_operands(references, res_stmt->operands_ref(), eval_ctx);
+        process_operands(references_buffer, res_stmt->operands_ref(), eval_ctx);
     }
     else
         return false;
 
-    process_label(references, *label, eval_ctx);
+    process_label(references_buffer, *label, eval_ctx);
 
-    if (references.empty())
+    if (references_buffer.empty())
         return false;
 
-    trigger_attribute_lookahead(std::move(references), eval_ctx, listener);
+    trigger_attribute_lookahead(std::move(references_buffer), eval_ctx, listener);
 
     return true;
 }
 
-void statement_provider::trigger_attribute_lookahead(std::set<context::id_index> references,
+void statement_provider::trigger_attribute_lookahead(std::vector<context::id_index>&& references_buffer,
     const expressions::evaluation_context& eval_ctx,
     processing::processing_state_listener& listener)
 {
     auto&& [statement_position, snapshot] = eval_ctx.hlasm_ctx.get_begin_snapshot(false);
 
-    listener.start_lookahead(lookahead_start_data(std::move(references), statement_position, std::move(snapshot)));
+    std::sort(references_buffer.begin(), references_buffer.end());
+
+    listener.start_lookahead(lookahead_start_data(
+        std::vector(references_buffer.begin(), std::unique(references_buffer.begin(), references_buffer.end())),
+        statement_position,
+        std::move(snapshot)));
 }
 
-bool statement_provider::process_label(std::set<context::id_index>& symbols,
+bool statement_provider::process_label(std::vector<context::id_index>& symbols,
     const semantics::label_si& label,
     const expressions::evaluation_context& eval_ctx)
 {
@@ -95,7 +102,7 @@ bool statement_provider::process_label(std::set<context::id_index>& symbols,
     }
 }
 
-bool statement_provider::process_instruction(std::set<context::id_index>& symbols,
+bool statement_provider::process_instruction(std::vector<context::id_index>& symbols,
     const semantics::instruction_si& instruction,
     const expressions::evaluation_context& eval_ctx)
 {
@@ -107,7 +114,7 @@ bool statement_provider::process_instruction(std::set<context::id_index>& symbol
     return semantics::concatenation_point::get_undefined_attributed_symbols(symbols, chain, eval_ctx);
 }
 
-bool statement_provider::process_operands(std::set<context::id_index>& symbols,
+bool statement_provider::process_operands(std::vector<context::id_index>& symbols,
     const semantics::operands_si& operands,
     const expressions::evaluation_context& eval_ctx)
 {
diff --git a/parser_library/src/processing/statement_providers/statement_provider.h b/parser_library/src/processing/statement_providers/statement_provider.h
index 19cf37356..89f34fb46 100644
--- a/parser_library/src/processing/statement_providers/statement_provider.h
+++ b/parser_library/src/processing/statement_providers/statement_provider.h
@@ -46,23 +46,25 @@ class statement_provider
 protected:
     static bool try_trigger_attribute_lookahead(const semantics::instruction_si& instruction,
         expressions::evaluation_context eval_ctx,
-        processing::processing_state_listener& listener);
+        processing::processing_state_listener& listener,
+        std::vector<context::id_index>&& references_buffer);
     static bool try_trigger_attribute_lookahead(const context::hlasm_statement& statement,
         expressions::evaluation_context eval_ctx,
-        processing::processing_state_listener& listener);
+        processing::processing_state_listener& listener,
+        std::vector<context::id_index>&& references_buffer);
 
 private:
-    static void trigger_attribute_lookahead(std::set<context::id_index> references,
+    static void trigger_attribute_lookahead(std::vector<context::id_index>&& references_buffer,
         const expressions::evaluation_context& eval_ctx,
         processing::processing_state_listener& listener);
 
-    static bool process_label(std::set<context::id_index>& symbols,
+    static bool process_label(std::vector<context::id_index>& symbols,
         const semantics::label_si& label,
         const expressions::evaluation_context& eval_ctx);
-    static bool process_instruction(std::set<context::id_index>& symbols,
+    static bool process_instruction(std::vector<context::id_index>& symbols,
         const semantics::instruction_si& instruction,
         const expressions::evaluation_context& eval_ctx);
-    static bool process_operands(std::set<context::id_index>& symbols,
+    static bool process_operands(std::vector<context::id_index>& symbols,
         const semantics::operands_si& operands,
         const expressions::evaluation_context& eval_ctx);
 };
diff --git a/parser_library/src/semantics/concatenation.cpp b/parser_library/src/semantics/concatenation.cpp
index 109b72ce2..ee18416b3 100644
--- a/parser_library/src/semantics/concatenation.cpp
+++ b/parser_library/src/semantics/concatenation.cpp
@@ -213,7 +213,7 @@ const var_sym_conc* concatenation_point::find_var_sym(
 }
 
 bool concatenation_point::get_undefined_attributed_symbols(
-    std::set<context::id_index>& symbols, const concat_chain& chain, const expressions::evaluation_context& eval_ctx)
+    std::vector<context::id_index>& symbols, const concat_chain& chain, const expressions::evaluation_context& eval_ctx)
 {
     bool result = false;
     for (auto it = chain.begin(); it != chain.end(); ++it)
diff --git a/parser_library/src/semantics/concatenation.h b/parser_library/src/semantics/concatenation.h
index ffe69517f..71ec007fd 100644
--- a/parser_library/src/semantics/concatenation.h
+++ b/parser_library/src/semantics/concatenation.h
@@ -120,7 +120,7 @@ struct concatenation_point
 
     static const var_sym_conc* find_var_sym(concat_chain::const_iterator begin, concat_chain::const_iterator end);
 
-    static bool get_undefined_attributed_symbols(std::set<context::id_index>& symbols,
+    static bool get_undefined_attributed_symbols(std::vector<context::id_index>& symbols,
         const concat_chain& chain,
         const expressions::evaluation_context& eval_ctx);
 
diff --git a/parser_library/src/semantics/operand_impls.cpp b/parser_library/src/semantics/operand_impls.cpp
index 14928c420..41af6e9db 100644
--- a/parser_library/src/semantics/operand_impls.cpp
+++ b/parser_library/src/semantics/operand_impls.cpp
@@ -559,7 +559,7 @@ var_ca_operand::var_ca_operand(vs_ptr variable_symbol, range operand_range)
 {}
 
 bool var_ca_operand::get_undefined_attributed_symbols(
-    std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
+    std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
 {
     return expressions::ca_var_sym::get_undefined_attributed_symbols_vs(symbols, variable_symbol, eval_ctx);
 }
@@ -572,7 +572,7 @@ expr_ca_operand::expr_ca_operand(expressions::ca_expr_ptr expression, range oper
 {}
 
 bool expr_ca_operand::get_undefined_attributed_symbols(
-    std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
+    std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
 {
     return expression->get_undefined_attributed_symbols(symbols, eval_ctx);
 }
@@ -585,7 +585,7 @@ seq_ca_operand::seq_ca_operand(seq_sym sequence_symbol, range operand_range)
 {}
 
 bool seq_ca_operand::get_undefined_attributed_symbols(
-    std::set<context::id_index>&, const expressions::evaluation_context&)
+    std::vector<context::id_index>&, const expressions::evaluation_context&)
 {
     return false;
 }
@@ -599,7 +599,7 @@ branch_ca_operand::branch_ca_operand(seq_sym sequence_symbol, expressions::ca_ex
 {}
 
 bool branch_ca_operand::get_undefined_attributed_symbols(
-    std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
+    std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx)
 {
     return expression->get_undefined_attributed_symbols(symbols, eval_ctx);
 }
diff --git a/parser_library/src/semantics/operand_impls.h b/parser_library/src/semantics/operand_impls.h
index b747315e4..cd5116c8b 100644
--- a/parser_library/src/semantics/operand_impls.h
+++ b/parser_library/src/semantics/operand_impls.h
@@ -411,7 +411,7 @@ struct ca_operand : operand
     const branch_ca_operand* access_branch() const;
 
     virtual bool get_undefined_attributed_symbols(
-        std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) = 0;
+        std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) = 0;
 
     const ca_kind kind;
 };
@@ -422,7 +422,7 @@ struct var_ca_operand final : ca_operand
     var_ca_operand(vs_ptr variable_symbol, const range operand_range);
 
     bool get_undefined_attributed_symbols(
-        std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
+        std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
 
     vs_ptr variable_symbol;
 
@@ -436,7 +436,7 @@ struct expr_ca_operand final : ca_operand
 
 
     bool get_undefined_attributed_symbols(
-        std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
+        std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
 
     expressions::ca_expr_ptr expression;
 
@@ -450,7 +450,7 @@ struct seq_ca_operand final : ca_operand
 
 
     bool get_undefined_attributed_symbols(
-        std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
+        std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
 
     seq_sym sequence_symbol;
 
@@ -464,7 +464,7 @@ struct branch_ca_operand final : ca_operand
 
 
     bool get_undefined_attributed_symbols(
-        std::set<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
+        std::vector<context::id_index>& symbols, const expressions::evaluation_context& eval_ctx) override;
 
     seq_sym sequence_symbol;
     expressions::ca_expr_ptr expression;
diff --git a/parser_library/test/expressions/ca_constant_test.cpp b/parser_library/test/expressions/ca_constant_test.cpp
index 944f69356..66b7ab751 100644
--- a/parser_library/test/expressions/ca_constant_test.cpp
+++ b/parser_library/test/expressions/ca_constant_test.cpp
@@ -31,7 +31,7 @@ TEST(ca_constant, undefined_attributes)
 
     ca_constant c(1, range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(c.get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), 0U);
 }
diff --git a/parser_library/test/expressions/ca_expr_list_test.cpp b/parser_library/test/expressions/ca_expr_list_test.cpp
index 9258fa723..c5d103fc1 100644
--- a/parser_library/test/expressions/ca_expr_list_test.cpp
+++ b/parser_library/test/expressions/ca_expr_list_test.cpp
@@ -100,7 +100,7 @@ TEST(ca_expr_list, get_undefined_attributed_symbols)
 
     diagnostic_op_consumer_container diags;
     evaluation_context eval_ctx { ctx, library_info_transitional::empty, diags };
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_TRUE(expr_list.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_GT(references.size(), 0);
diff --git a/parser_library/test/expressions/ca_function_test.cpp b/parser_library/test/expressions/ca_function_test.cpp
index 2f1d33fee..d7b1bc9b8 100644
--- a/parser_library/test/expressions/ca_function_test.cpp
+++ b/parser_library/test/expressions/ca_function_test.cpp
@@ -62,7 +62,10 @@ class set_expr final : public ca_expression
         , value(std::move(value))
     {}
 
-    bool get_undefined_attributed_symbols(undef_sym_set&, const evaluation_context&) const override { return false; };
+    bool get_undefined_attributed_symbols(std::vector<context::id_index>&, const evaluation_context&) const override
+    {
+        return false;
+    }
 
     void resolve_expression_tree(ca_expression_ctx, diagnostic_op_consumer&) override {}
 
diff --git a/parser_library/test/expressions/ca_string_test.cpp b/parser_library/test/expressions/ca_string_test.cpp
index 6ef703d72..4823a8bf3 100644
--- a/parser_library/test/expressions/ca_string_test.cpp
+++ b/parser_library/test/expressions/ca_string_test.cpp
@@ -44,7 +44,7 @@ TEST(ca_string, undefined_attributes)
 
     ca_string s(std::move(value), std::move(dupl), std::move(substr), range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(s.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_EQ(references.size(), 0U);
diff --git a/parser_library/test/expressions/ca_symbol_attribute_test.cpp b/parser_library/test/expressions/ca_symbol_attribute_test.cpp
index ce0952864..6e3e569db 100644
--- a/parser_library/test/expressions/ca_symbol_attribute_test.cpp
+++ b/parser_library/test/expressions/ca_symbol_attribute_test.cpp
@@ -40,7 +40,7 @@ TEST(ca_symbol_attr, undefined_attributes)
 
     ca_symbol_attribute attr(std::move(vs), context::data_attr_kind::D, range(), range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(attr.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_EQ(references.size(), 0U);
diff --git a/parser_library/test/expressions/ca_symbol_test.cpp b/parser_library/test/expressions/ca_symbol_test.cpp
index d12cb925e..c2a1cfcfd 100644
--- a/parser_library/test/expressions/ca_symbol_test.cpp
+++ b/parser_library/test/expressions/ca_symbol_test.cpp
@@ -32,7 +32,7 @@ TEST(ca_symbol, undefined_attributes)
 
     ca_symbol sym(context::id_index("N"), range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(sym.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_EQ(references.size(), 0U);
diff --git a/parser_library/test/expressions/ca_var_sym_test.cpp b/parser_library/test/expressions/ca_var_sym_test.cpp
index 9f997f522..bc23c4b9b 100644
--- a/parser_library/test/expressions/ca_var_sym_test.cpp
+++ b/parser_library/test/expressions/ca_var_sym_test.cpp
@@ -40,7 +40,7 @@ TEST(ca_var_sym_basic, undefined_attributes)
 
     ca_var_sym var(std::move(vs), range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(var.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_EQ(references.size(), 0U);
@@ -64,7 +64,7 @@ TEST(ca_var_sym_created, undefined_attributes)
 
     ca_var_sym var(std::move(vs), range());
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(var.get_undefined_attributed_symbols(references, eval_ctx));
 
     EXPECT_EQ(references.size(), 0U);
diff --git a/parser_library/test/processing/lookahead_test.cpp b/parser_library/test/processing/lookahead_test.cpp
index 03fb9913c..8480b67bc 100644
--- a/parser_library/test/processing/lookahead_test.cpp
+++ b/parser_library/test/processing/lookahead_test.cpp
@@ -219,7 +219,7 @@ TEST(attribute_lookahead, lookup_triggered)
     diagnostic_op_consumer_container diags;
     evaluation_context eval_ctx { a.hlasm_ctx(), library_info_transitional::empty, diags };
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_TRUE(expr->get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), (size_t)1);
 
@@ -240,10 +240,10 @@ TEST(attribute_lookahead, nested_lookup_triggered)
     auto v2 = a.hlasm_ctx().create_local_variable<context::C_t>(id_index("V2"), true);
     v2->access_set_symbol<context::C_t>()->set_value("B");
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_TRUE(expr->get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), (size_t)1);
-    EXPECT_TRUE(references.find(id_index("B")) != references.end());
+    EXPECT_EQ(std::count(references.begin(), references.end(), id_index("B")), 1);
 
     a.hlasm_ctx().ord_ctx.add_symbol_reference(
         context::symbol(id_index("B"),
@@ -256,7 +256,7 @@ TEST(attribute_lookahead, nested_lookup_triggered)
     references.clear();
     EXPECT_TRUE(expr->get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), (size_t)1);
-    EXPECT_TRUE(references.find(id_index("A")) != references.end());
+    EXPECT_EQ(std::count(references.begin(), references.end(), id_index("A")), 1);
 
     EXPECT_EQ(a.diags().size(), (size_t)0);
 }
@@ -279,7 +279,7 @@ TEST(attribute_lookahead, lookup_not_triggered)
     ASSERT_TRUE(tmp);
 
     // although length is undefined the actual symbol is defined so no lookup should happen
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_FALSE(expr->get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), (size_t)0);
 
@@ -295,7 +295,7 @@ TEST(attribute_lookahead, lookup_of_two_refs)
     diagnostic_op_consumer_container diags;
     evaluation_context eval_ctx { a.hlasm_ctx(), library_info_transitional::empty, diags };
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_TRUE(expr->get_undefined_attributed_symbols(references, eval_ctx));
     EXPECT_EQ(references.size(), (size_t)2);
 
@@ -311,9 +311,9 @@ TEST(attribute_lookahead, lookup_of_two_refs_but_one_symbol)
     diagnostic_op_consumer_container diags;
     evaluation_context eval_ctx { a.hlasm_ctx(), library_info_transitional::empty, diags };
 
-    std::set<context::id_index> references;
+    std::vector<context::id_index> references;
     EXPECT_TRUE(expr->get_undefined_attributed_symbols(references, eval_ctx));
-    EXPECT_EQ(references.size(), (size_t)1);
+    EXPECT_EQ(references.size(), (size_t)2);
 
     EXPECT_EQ(a.diags().size(), (size_t)0);
 }