[hierarch] subclasses of graphical walk
- a
trailis awalkin which alledgesare distinct - a
pathis atrailin which allnodesare distinct - a
cycleis atrailin which the 1st and the last node are the same
trail is a walk in which all edges are distinctpath is a trail in which all nodes are distinctcycle is a trail in which the 1st and the last node are the same