Figure 2

Example of contraction by CompressVertices Example of contraction of identical sets of vertices and the edges between the vertices by CompressVertices. (A) Graph with 7 vertices and 8 edges. (B) Candidate vertices {' a', 'b', 'c '} and three edges ('a', 'b'), ('b', 'c'), and ('c', 'a') to be contracted. (C) Candidate vertices {'a', 'b', 'b'} and two edges of ('a', 'b') to be contracted. (D) Graph contracted from graph (A) by substituting vertices {'a', 'b', 'b'} and the edges with 'abb'.