code for unevaluated Boolean and conditional expressions

Hi Mario,

> Question: is Macavity responsible for the crime?

I'm glad to see Maxima is capable of handling this
oh-so-very-important problem ... 8^)

The "=>" function is susceptible to a kind error which exists
without boolsimp, but for better or worse boolsimp makes it easier
to bump into it. With the declaration

 "=>"(r,s):= not r or s $

then something like (not r) => foo causes a stack overflow.
A simpler example of the same phenomenon without boolsimp:

  foo (x) := not x;
  foo ('(not x)); => stack overflow

This behavior is a consequence of dynamic binding --
the symbol x is bound to an expression containing x, and the attempt
to evaluate it leads to an bottomless recursion.

A work around is to avoid name collisions, e.g define the function
with an unlikely argument name like x% instead of x.
That's not a very satisfactory solution.

best,
Robert