Figure 1

Example of contraction of identical edges. (A) Graph with 7 vertices and 8 edges. (B, C) Graphs contracted from graph (A) by GRAPHITOUR. (D) Graph contracted from graph (A) by our proposed method. (E) Graph contracted from graph (A) by substituting two edges ('a', 'a') and ('a', 'b') with 'aab'. (F) Graph contracted from graph (A) by substituting three vertices and the edges between the vertices with 'aab'.