Comment #2 on issue 2007 by asmeurer: (exp(exp(x))).atoms(exp)
http://code.google.com/p/sympy/issues/detail?id=2007
Well, I think I remember Chris implementing something where if you pass an
argument to atoms, then it gives you all the terms that match that, like:
(sin(x + 1) + sin(x)*cos(x)).atoms(sin)
set(sin(x), sin(1 + x))
I need something like this for building the tower of differential
extensions for the integration algorithm so that, for example, if an
expression has exp(x), exp(2*x) and exp(x/2) all in it somewhere, I make
sure to choose the extension t = exp(x/2) so that exp(x) == t**2 and
exp(2*x) == t**4. Otherwise, if I choose one of the other ones, say t =
exp(x), then exp(x/2) == sqrt(t) will be algebraic, which we must avoid.
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