#5276 assume(x > 2); is(2^x > 4) -> unknown

[David Scherfgen]

Another severe limitation of sign:

(%i1) assume(x > 2)$

(%i2) is(2^x > 4);
(%o2) unknown

This should also work for other increasing or decreasing functions when an inverse exists.
In the example, the 4 should be rewritten as 2^2, and then it's just a matter of comparing the exponents.