diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/Class.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/Class.kt
index c106a8de..df8c0f64 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/Class.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/Class.kt
@@ -45,7 +45,7 @@ interface Class {
          * @throws IllegalArgumentException if the name is blank
          */
         fun create(name: String): Class {
-            check(name.isNotBlank()) { "name cannot be blank" }
+            require(name.isNotBlank()) { "name cannot be blank" }
             return ClassImpl(name)
         }
     }
diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/School.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/School.kt
index 3d0152a7..b2e4fb67 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/School.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/School.kt
@@ -61,8 +61,8 @@ interface School {
          * @throws IllegalArgumentException if the name or the city is blank
          */
         fun create(name: String, city: String): School {
-            check(name.isNotBlank()) { "name cannot be blank" }
-            check(city.isNotBlank()) { "city cannot be blank" }
+            require(name.isNotBlank()) { "name cannot be blank" }
+            require(city.isNotBlank()) { "city cannot be blank" }
             return SchoolImpl(name, city)
         }
     }
diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/calendar/CalendarEventFactory.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/calendar/CalendarEventFactory.kt
index 10788c55..54d15c61 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/calendar/CalendarEventFactory.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/calendar/CalendarEventFactory.kt
@@ -108,13 +108,13 @@ object CalendarEventFactory {
         subject: Subject,
         module: String? = null,
     ): WeekLesson {
-        check(subject.isNotBlank()) {
+        require(subject.isNotBlank()) {
             "subject cannot be blank"
         }
-        check(!startTime.isAfter(endTime)) {
+        require(!startTime.isAfter(endTime)) {
             "startTime cannot be after endTime"
         }
-        check(!fromDate.isAfter(toDate)) {
+        require(!fromDate.isAfter(toDate)) {
             "fromDate cannot be after toDate"
         }
         return WeekLessonImpl(
@@ -152,10 +152,10 @@ object CalendarEventFactory {
         subject: Subject,
         module: String? = null,
     ): DateLesson {
-        check(subject.isBlank()) {
+        require(subject.isNotBlank()) {
             "subject cannot be blank"
         }
-        check(startTime.isAfter(endTime)) {
+        require(!startTime.isAfter(endTime)) {
             "startTime cannot be after endTime"
         }
         return DateLessonImpl(
diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/implementation/ClassImpl.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/implementation/ClassImpl.kt
index 8fe9172f..e63f4240 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/implementation/ClassImpl.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/implementation/ClassImpl.kt
@@ -33,12 +33,11 @@ internal data class ClassImpl(
      * @throws IllegalArgumentException if the student is already in the class or if the student is not in the class
      */
     override fun addStudent(student: Student): Class {
-        if (students.contains(student)) {
-            error("student is already in this class")
-        } else {
-            return copy().apply {
-                students = students + student
-            }
+        require(!students.contains(student)) {
+            "student is already in this class"
+        }
+        return copy().apply {
+            students = students + student
         }
     }
 
@@ -51,21 +50,20 @@ internal data class ClassImpl(
      * @throws IllegalArgumentException if the professor is not in the class or if the professor doesn't teach the subjects in the class
      */
     override fun addProfessor(professor: Professor, subjects: Set<Subject>): Class {
-        if (subjects.isEmpty()) {
-            error("subjects cannot be empty")
+        require(subjects.isNotEmpty()) {
+            "subjects cannot be empty"
+        }
+        val newClass = if (professors.contains(professor)) {
+            val oldSubjects = professorTeachSubjects[professor] ?: error("professor is not in this class")
+            copy().apply {
+                professorTeachSubjects = professorTeachSubjects + (professor to oldSubjects + subjects)
+            }
         } else {
-            val newClass = if (professors.contains(professor)) {
-                val oldSubjects = professorTeachSubjects[professor] ?: error("professor is not in this class")
-                copy().apply {
-                    professorTeachSubjects = professorTeachSubjects + (professor to oldSubjects + subjects)
-                }
-            } else {
-                copy().apply {
-                    professors = professors + professor
-                    professorTeachSubjects = professorTeachSubjects + (professor to subjects)
-                }
+            copy().apply {
+                professors = professors + professor
+                professorTeachSubjects = professorTeachSubjects + (professor to subjects)
             }
-            return newClass
         }
+        return newClass
     }
 }
diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Professor.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Professor.kt
index 399ba0cf..c3853837 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Professor.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Professor.kt
@@ -33,9 +33,9 @@ interface Professor : Person {
             name: String,
             surname: String,
         ): Professor {
-            check(email.isNotBlank()) { "email cannot be blank" }
-            check(name.isNotBlank()) { "name cannot be blank" }
-            check(surname.isNotBlank()) { "surname cannot be blank" }
+            require(email.isNotBlank()) { "email cannot be blank" }
+            require(name.isNotBlank()) { "name cannot be blank" }
+            require(surname.isNotBlank()) { "surname cannot be blank" }
             return ProfessorImpl(email, name, surname)
         }
     }
diff --git a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Student.kt b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Student.kt
index 8fc3b0ea..0c58bd3d 100644
--- a/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Student.kt
+++ b/schoolDomain/src/main/kotlin/com/intelligentbackpack/schooldomain/entities/person/Student.kt
@@ -30,9 +30,9 @@ interface Student : Person {
             name: String,
             surname: String,
         ): Student {
-            check(email.isNotBlank()) { "email cannot be blank" }
-            check(name.isNotBlank()) { "name cannot be blank" }
-            check(surname.isNotBlank()) { "surname cannot be blank" }
+            require(email.isNotBlank()) { "email cannot be blank" }
+            require(name.isNotBlank()) { "name cannot be blank" }
+            require(surname.isNotBlank()) { "surname cannot be blank" }
             return StudentImpl(email, name, surname)
         }
     }