A path in $M$ from a vertex $i$ to a vertex $j$ is a finite sequence $(e_1, \ldots ,e_m)$ of oriented edges such that $\textrm{end}(e_k) = \textrm{start}(e_{k+1})$ and $\textrm{start}(e_{1})=i$, $\textrm{end}(e_m) =j$. A surface is called connected if for any two … Continue reading Paths and connectivity