El Instituto "Jorge Juan" de Matemáticas del CSIC se integraría posteriormente en el Instituto de Matemáticas y Física Fundamental (IMAFF).J.C. Mathews and D.W. Curtis have introduced some structures which generalize structures of uniform types to the product of two sets, and they obtain a generalized version of Banach's contraction mapping theorem. In this note we prove that these structures are obtained from the usual analogues by means of a particular bijection; hence we do not have a meaningful generalization. For example, this bijection provides, from a result by A. S. Davies, an analogue of Banach's well-known contraction mapping theorem which trivially implies the main result of [4].Peer reviewed