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I was looking at their documentation:

> For example, Axiom's integrator gives you the answer when an answer exists. If one does not, it provides a proof that there is no answer. Integration is just one of a multitude of symbolic operations that Axiom provides.

What does "an answer exists" in this case? Is axiom able to prove that an integral does not have an answer mathematically, which seems impressive, or just that it can not be found using its own substitucion rules?