more than once. A trail is a sequence of consecutively linked edges in which no edge can appear Unlike a path, a vertex can be visited any number of times in a trail. A cycle is a trail that starts and ends at the same vertex. A cycle that repeats no vertices is a circuit. a. Show that a subset of the vertices on a trail from z to y can be used to make a path from a to b. Prove or give a counter-example: If a and y lie on a cycle, then they must lie on a circuit. Find a graph with more than one vertex that is isomorphic to its own complement. y