For normal lisp implementations, allowing names to appear in their own definitions requires lexical environment frame to be mutable, which breaks the assumption

For normal lisp implementations, allowing names to appear in their own definitions requires lexical environment frame to be mutable, which breaks the assumption that all notionally on-heap objects are immutable. This observation is somewhat relevant to the weird semantics of "lexical" scoping in Python, because the obvious semantics would cause cycle between frame object and function defined in it's scope.