TSIMP is used to minimize the number of rational ``variables''.
It may be used if RISCH fails because
it returns an expression which is ``weak-normalized''.
Note that TSIMP considers trigonometric functions as
complex exponentials,
and simplifies them this way and that the output of TSIMP
is affected by the state of the flag 13 (complex flag): if flag 13 is
cleared, then complex logarithms and exponentials are converted
to arctan and sin/cos functions.