Contractions:: Nijenhuis and Saletan tensors for general algebraic structures

We study generalizations in many directions of the contraction procedure for Lie algebras introduced by Saletan, We consider products of an arbitrary nature, not necessarily Lie brackets, and we generalize to infinite dimension, considering a modification of the approach by Nijenhuis tensors to bilinear operations on sections of finite-dimensional vector bundles. We apply our general procedure to Lie algebras, Lie algebroids and Poisson brackets. We also present results on contractions of n-ary products and coproducts.