Doctest: Incorrect zero test of complex symbolic expressions

[mezzarobba]

This is fixed but needs a doctest:

Yet another example where symbolic expressions are abusively considered equivalent, even though simplify() has become a bit more careful.

sage: var('a,x')
(a, x)
sage: assume(a, 'complex')
sage: assume(x, 'complex')
sage: expr = a^(4*x) - (a^4)^x
sage: expr.is_zero()
True
sage: expr(a=I, x=1/2)
-2

Component: symbolics

Author: Ralf Stephan

Branch/Commit: 9974eef

Reviewer: Karl-Dieter Crisman

Issue created by migration from https://trac.sagemath.org/ticket/15571

[rwst]

comment:4

Appears to having been fixed and also already included in Sage.

[rwst]

Description changed:

--- 
+++ 
@@ -1,3 +1,5 @@
+This is fixed but needs a doctest:
+
 Yet another example where symbolic expressions are abusively considered equivalent, even though `simplify()` has become a bit more careful.
 
 ```