diff --git a/src/ytdl_sub/script/script.py b/src/ytdl_sub/script/script.py
index e3341f6d..53d3dc02 100644
--- a/src/ytdl_sub/script/script.py
+++ b/src/ytdl_sub/script/script.py
@@ -4,7 +4,6 @@ from typing import List
 from typing import Optional
 from typing import Set
 
-from ytdl_sub.script.functions import Functions
 from ytdl_sub.script.parser import parse
 from ytdl_sub.script.types.resolvable import Resolvable
 from ytdl_sub.script.types.syntax_tree import SyntaxTree
@@ -145,12 +144,6 @@ class Script:
                         f"{nested_custom_function.num_input_args}"
                     )
 
-    def _ensure_lambda_usage_num_input_arguments_valid(self) -> None:
-        for variable_name, variable_definition in self._variables.items():
-            for lambda_argument in variable_definition.lambda_arguments:
-                if Functions.is_built_in(name=lambda_argument.value):
-                    pass
-
     def _validate(self) -> None:
         self._ensure_no_custom_function_cycles()
         self._ensure_custom_function_arguments_valid()
diff --git a/src/ytdl_sub/script/types/function.py b/src/ytdl_sub/script/types/function.py
index a1309bed..34fd8a47 100644
--- a/src/ytdl_sub/script/types/function.py
+++ b/src/ytdl_sub/script/types/function.py
@@ -12,6 +12,7 @@ from ytdl_sub.script.functions import Functions
 from ytdl_sub.script.types.array import ResolvedArray
 from ytdl_sub.script.types.array import UnresolvedArray
 from ytdl_sub.script.types.resolvable import Argument
+from ytdl_sub.script.types.resolvable import BuiltInFunctionType
 from ytdl_sub.script.types.resolvable import FunctionType
 from ytdl_sub.script.types.resolvable import Lambda
 from ytdl_sub.script.types.resolvable import NamedCustomFunction
@@ -19,7 +20,6 @@ from ytdl_sub.script.types.resolvable import Resolvable
 from ytdl_sub.script.types.resolvable import ReturnableArgument
 from ytdl_sub.script.types.resolvable import ReturnableArgumentA
 from ytdl_sub.script.types.resolvable import ReturnableArgumentB
-from ytdl_sub.script.types.resolvable import TypeHintedFunctionType
 from ytdl_sub.script.types.variable import FunctionArgument
 from ytdl_sub.script.types.variable import Variable
 from ytdl_sub.script.types.variable_dependency import VariableDependency
@@ -78,7 +78,7 @@ class CustomFunction(Function, NamedCustomFunction):
         raise UNREACHABLE
 
 
-class BuiltInFunction(Function, TypeHintedFunctionType):
+class BuiltInFunction(Function, BuiltInFunctionType):
     def validate_args(self) -> "BuiltInFunction":
         if not self.function_spec.is_compatible(input_args=self.args):
             raise FunctionArgumentsExceptionFormatter(
diff --git a/src/ytdl_sub/script/types/resolvable.py b/src/ytdl_sub/script/types/resolvable.py
index 7282393b..e38f7f7b 100644
--- a/src/ytdl_sub/script/types/resolvable.py
+++ b/src/ytdl_sub/script/types/resolvable.py
@@ -142,7 +142,7 @@ class FunctionType(NamedArgument, ABC):
 
 
 @dataclass(frozen=True)
-class TypeHintedFunctionType(FunctionType, ABC):
+class BuiltInFunctionType(FunctionType, ABC):
     @abstractmethod
     def output_type(self) -> Type[Resolvable]:
         pass
diff --git a/src/ytdl_sub/script/utils/exception_formatters.py b/src/ytdl_sub/script/utils/exception_formatters.py
index 54499e48..2cdd2244 100644
--- a/src/ytdl_sub/script/utils/exception_formatters.py
+++ b/src/ytdl_sub/script/utils/exception_formatters.py
@@ -4,8 +4,8 @@ from typing import Type
 from typing import TypeVar
 from typing import Union
 
+from ytdl_sub.script.types.resolvable import BuiltInFunctionType
 from ytdl_sub.script.types.resolvable import NamedType
-from ytdl_sub.script.types.resolvable import TypeHintedFunctionType
 from ytdl_sub.script.utils.exceptions import IncompatibleFunctionArguments
 from ytdl_sub.script.utils.exceptions import UserException
 from ytdl_sub.script.utils.type_checking import FunctionSpec
@@ -101,7 +101,7 @@ class FunctionArgumentsExceptionFormatter:
     def __init__(
         self,
         input_spec: FunctionSpec,
-        function_instance: TypeHintedFunctionType,
+        function_instance: BuiltInFunctionType,
     ):
         self._args = input_spec.args
         self._varargs = input_spec.varargs
@@ -126,7 +126,7 @@ class FunctionArgumentsExceptionFormatter:
     def _received_args_str(self) -> str:
         received_type_names: List[str] = []
         for arg in self._input_args:
-            if isinstance(arg, TypeHintedFunctionType):
+            if isinstance(arg, BuiltInFunctionType):
                 if is_union(arg.output_type()):
                     received_type_names.append(
                         f"%{arg.name}(...)->Union["
diff --git a/src/ytdl_sub/script/utils/type_checking.py b/src/ytdl_sub/script/utils/type_checking.py
index 4c923c1d..c7f6c0e7 100644
--- a/src/ytdl_sub/script/utils/type_checking.py
+++ b/src/ytdl_sub/script/utils/type_checking.py
@@ -9,11 +9,11 @@ from typing import Union
 from typing import get_origin
 
 from ytdl_sub.script.types.resolvable import Argument
+from ytdl_sub.script.types.resolvable import BuiltInFunctionType
 from ytdl_sub.script.types.resolvable import FunctionType
 from ytdl_sub.script.types.resolvable import Lambda
 from ytdl_sub.script.types.resolvable import NamedType
 from ytdl_sub.script.types.resolvable import Resolvable
-from ytdl_sub.script.types.resolvable import TypeHintedFunctionType
 from ytdl_sub.script.types.variable import Variable
 from ytdl_sub.script.utils.exceptions import UNREACHABLE
 
@@ -57,7 +57,7 @@ def is_type_compatible(
     True if arg is compatible with expected_arg_type. False otherwise.
     """
     arg_type: Type[NamedType] = arg.__class__
-    if isinstance(arg, FunctionType) and isinstance(arg, TypeHintedFunctionType):
+    if isinstance(arg, BuiltInFunctionType):
         arg_type = arg.output_type()  # built-in function
     elif isinstance(arg, FunctionType):
         return True  # custom-function, can be anything, so pass for now