Given the simple graph as shown below is the altering sequence v1 a1 v2 a5 v3 a3 v4 a4 v2 a1 v1 a httpscorexjtlueducnpluginfilephp535211questionquestiontext244481291221436Q_AlteringSeq_Walk2png

The altering sequence represents a walk on the given graph. Starting from vertex v1, we follow edge a1 to vertex v2, then edge a5 to vertex v3, then edge a3 to vertex v4, then edge a4 back to vertex v2, then edge a1 back to vertex v1. The final part of the sequence, "a", is incomplete and does not represent a valid edge in the graph.