I'd expect aliens to have discovered their equivalent of the Church-Turing thesis, Tarski's externality of truth, Godel's incompleteness theorems, etc. That wo

I'd expect aliens to have discovered their equivalent of the Church-Turing thesis, Tarski's externality of truth, Godel's incompleteness theorems, etc. That would give them a strong ability to model our mathematics within their own and see its computational structure and begin finding correspondences to theirs. Similarly, we could begin modeling their conception of mathematics in a similar way and as soon as we both have arrived at a morphism between our representation and theirs of some particular theorem we could grow our knowledge and understanding of the other. The key is that mathematics flows from logic and logic flows from computation and computation is universal.