genusOf :: (SurfaceDiagram a) => a t -> Int
genusOf a = (2 - eulerCharOf a) `div` 2
genusOf :: (SurfaceDiagram a) => a t -> Int
genusOf a = (2 - eulerCharOf a) `div` 2
genusOf a = (2 - eulerCharOf a) `div` 2