Comment #25 on issue 2039 by asmeurer: Mul.eval_subs problems
http://code.google.com/p/sympy/issues/detail?id=2039

Is there a reason not to make the hint assume_positive rather than assume_pos_real?

In logcombine(), it's called assume_pos_real because for the combination rules to be valid, the exponents have to be real and the arguments have to be positive. I wonder if we should just call it symbolic=True, which is what Maple does (http://www.maplesoft.com/support/help/Maple/view.aspx?path=combine%2fln).

And perhaps powdenest should be incorporated into powsimp as the exponent handler?
And then powsimp would get the assume hint.

Well, I agree powsimp should have an assume hint, since it is already blocked on certain combinations if I am correct. But I was thinking that powdenest() should be a separate function in simplify.py. The problem is that the combine hint to powsimp would become complicated for three different kinds of combination. If you think you can make it work, go for it, but to me, it seems keeping it separate would be much simpler.

I made powdenest respect assumptions that are already present:

I don't care either way about this. It seems that maybe, at least for when the user calls it manually from simplify.py, that it should split up the args. I know that it *does* need to split up the factors of an expression, as in powdenest(sqrt(x**2*(1 + y)**4)), though maybe it should require a manual call to factor() or sqf() first.

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