Earlier quoted context omitted.
Mathematica is literally the worst PL I've ever used, especially since you effectively have to use their built-in editor that doesn't even have multiple undo. Of course, it is the least-worst symbolic system out there currently. But, it's not like lisp wouldn't have developed similar capabilities if Mathematica didn't come around.
You mean like Macsyma, now Maxima, where he probably got some early ideas from?
https://groups.google.com/d/msg/comp.lang.lisp/BUxXH76CYdc/I...