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Coalescence of Difans and Diwheels Diego Bravo and Juan Rada Departamento de Matem a-acute t icas comma Facultad de Ciencias Universidad de Los Andes comma 5 101 M acute-e rida comma Venezuela dbravo at ula period ve comma juanrada at ula period ve Abstract period.. A directed graph G is nonderogatory if its adjacency matrix A is nonderogatory comma i period e period comma the characteristic polynomial of A is equal to the minimal polynomial of A period We analyze the problem whether the coalescence of difans and diwheels is nonderogatory period Also comma a formula for the characteristic polynomial of the coalescence of two directed graphs is presented period 2000 Mathematics Subject Classification: 5 C 50