Elliptic difference singular perturbations

Summary Difference approximations for differential singular perturbations with small parameter ɛ are considered. We point out ellipticity and coerciveness conditions which arenecessary andsufficient for a two-sided a priori estimate to hold for the solution of difference singular perturbation uniformly with respect to the ratio of both small parameters: the original one ɛ and the meshsize h. Entrata in Redazione il 27 maggio 1978.