Systems of arcs on a torus with two punctures

Abstract

For a compact surface $ S $ with a finite set of marked points $ P $, we define a 1-system to be a collection of arcs which are pairwise non-homotopic and intersect pairwise at most once. We prove that, up to equivalence, there are exactly 23 maximal 1-systems on $ (S, P) $ when $ S $ is a torus and $ |P| = 2 $. Along the way, we generalize some of the results of a previous paper to the context of surfaces with boundary. In particular, we prove that the maximal cardinality of a 1-system on $ (S, P) $ is $ 2 |\chi| (|\chi| + 1) - \frac{v}{2} $, where $ \chi $ is the Euler characteristic of $ (S, P) $ and $ v $ is the number of marked points of $ P $ in the boundary of $ S $.