Institution: | (1) Dpto. de Matemáticas y Computación, Facultad de Ciencias, Universidad del Zulia, Ap. 527, Maracaibo, Venezuela;(2) Dpto. de Computación, Universidad Central de Venezuela, Ap. 47002, Caracas, 1041-A, Venezuela;(3) Department of Mathematics and Computer Science, Austin Peay State University, Clarksville, TN 37044, USA;(4) Department of Mathematics, University of Kentucky, Lexington, KY 40506, USA |