#3865 crash from taking limit of factorial(x) + 1

[Dave Morris]

As pointed out in sagemath trac ticket #31762, the following simple limit results in an error that "Maxima encountered a Lisp error: Binding stack exhausted":
(%i1) limit(factorial(x) + 1, x, 0);
(I seem to be using Maxima version: 5.43.0 (x86_64-apple-darwin13.4.0) / Lisp: SBCL 1.5.3.)

[Robert Dodier]

Confirmed with current version (post-5.45).

For the record, a stack trace shows TOPLEVEL-$LIMIT --> LIMIT --> SIMPLIMIT --> SIMPLIMPLUS --> SIMPLIMPLUS1 --> SIMPAB --> SIMPINF --> SIMPINF-IC --> TOPLEVEL-$LIMIT.

Looks like the original limit as x --> 0 is replaced by limit as 1/x --> inf and then back again. I guess we have to figure out how to tell that there's no point is doing the transformation a second time, if the first didn't help.

[Barton Willis]

Inserting a call to ridoab early on eliminates this bug. I'm not sure it's the right fix:

(defun simplimfact (expr var val)
  (let* ((arglim (limit (cadr expr) var val 'think)) ; Limit of the argument.
         (arg2 arglim))
    (setq arglim (ridofab arglim))  ;; New line!

[Dan Gildea]

Fixed by [3456f42f2889215b0e5c260bdc65ad74e28128ae]