#2182 subst does not accept logical expressions

[Andrej Vodopivec]

This is OK:

(%i42) subst(not p,p,p);
(%o42) not p

This is not be an error:

(%i43) subst(p=not p, p);
incorrect syntax: Found logical expression where algebraic expression expected
subst(p=not p,
^

But subst accepts this:

(%i43) subst(p="not"(p), p);
(%o43) not p

[Andrej Vodopivec]

Actually, this is not related to subst:

(%i1) p = not q;
incorrect syntax: Found logical expression where algebraic expression expected