
Abstract: In this talk I will try to give an introduction to Aubry-Mather theory. Aubry-Mather theory can be described as a variational method for finding quasi-periodic solutions of Hamiltonian twist maps and monotone recurrence relations. We will start with a review of elementary results on circle homeomorphisms and from there
we move on to more to more complicated problems. I will end with a theorem of Blaz Mramor and myself on the non-existence of invariant quasi-periodic solutions (a so-called "converse KAM theorem").