Congruence of Two Vertices
Within three colors, two vertices (p, q)V(G) can be in one of the congruence relation defined as: congruent c(p) ≅ c(q), the resulting color c(q) always equals the selected color for c(p). anti-congruent c(p) c(q), <p, q>E, the resulting color c(q) always differs from the selected color for p. See figure 9 for an example of anti-congruence.
The third alternative when the colors of vertices are independent of each other is not used.
Let circuit Cf be defined: Cf = ∪(∆(E(C)) (CNf), and graph …show more content…
Proof. A G1L graph 3-coloring may not be feasible, regardless of the sub-rim vertices colors, when exist two connected congruent vertices. Sub-graph G1L received from F[5], denoted by G1F, is such and the only …show more content…
Let investigate graph G2TR under what circumstances its derived G1L will have a congruence conflict. A cycle Cf' that exhibits conflict is a C5 cycle with vertex v congruent to connected vertices p, q either within rim Ry or Rx. The cycle Cf' cannot be of an even length or C7+ cycle; the congruent vertices are not connected. More numerous presence of {f*} within P2R prevents from congruence of vertices within cycles {Cf} where fPy.
It is also impossible to have connected congruent vertices pRx and qRy since vertex p has no associated triangles to be congruent with another vertex. That means vertices s, t adjacent to p, q respectively would be within the same rim Ry as color reduced vertex f. However in order to have triangles to carry the congruence, vertices s, t should not be included into rim Ry since they would have also CF color. Thus vertices should be within rim Rx. This is a clear contradiction of the requirements for vertices s, t.
That contradiction ceases to be a contradiction only if Cf' is exactly as Cf* within F. Vertices f, p, and q are required to form a triangle of diagonals to carry the congruence via edge adjacent