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graph has got a triangle whose sides have di erent colors

Source: 12-th Hungary-Israel Mathematical Competition 2001

April 16, 2007
inductiongraph theorycombinatorics proposedcombinatorics

Problem Statement

Here GnG_{n} denotes a simple undirected graph with nn vertices, KnK_{n} denotes the complete graph with nn vertices, Kn,mK_{n,m} the complete bipartite graph whose components have mm and nn vertices, and CnC_{n} a circuit with nn vertices. The number of edges in the graph GnG_{n} is denoted e(Gn)e(G_{n}). The edges of Kn(n3)K_{n}(n \geq 3) are colored with nn colors, and every color is used. Show that there is a triangle whose sides have different colors.