The bug:
(C1) tex(a^b);
$$
Error: |$b| is not of type (OR RATIONAL LISP:FLOAT).
(C2) load("e://unk_mactex.lisp");
Loading e://unk_mactex.lisp
Finished loading e://unk_mactex.lisp
(D2) e://unk_mactex.lisp
(C3) tex(a^b);
$$a^{b}$$
(D3) FALSE
(C4)
The fix: In tex-mexpt, change (towards the end of the function)
(if (< x 10)
(tex x (list "^")(cons "" r) 'mparen 'mparen)
to
(if (and (numberp x) (< x 10))
(tex x (list "^")(cons "" r) 'mparen 'mparen)
Barton