Complete the Altering Sequence in a Simple Graph

The altering sequence is a sequence of vertices and edges that alternate. Starting at 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. However, the final part of the sequence, 'a()', is incomplete and does not specify which edge to follow from v1. Therefore, the altering sequence cannot be completed with the given information.