Although Franz Inc supported Franz Lisp and developed Allegro Common Lisp, it is my impression they are distinct implementations. I can't find any hard evidence one way or another. Do you know?
A think FL just morphed into ACL by renaming, and probably some code changes, but not reimplementation, but not having been there, I’m not 100% sure. Since then, of course, it’s essentially a different implementation bvo many revs.
