[aap_]

No, that's definitely wrong. Initially they compiled LISP code into assembly by hand (when LISP still looked a lot like fortran) and the plan was to write a compiler in assembly to automate that. Instead, McCarthy came up with a way to express LISP code (aka M-expressions) as data (aka S-expressions) to give a definition the LISP semantics in LISP itself. Steve Russell then hand compiled this definition, and lo, they had a working interpreter of S-expressions. M-expressions were never implemented and the compiler was written in LISP instead of assembly.