Behavior of bivariate interpolation operators at points of discontinuity   of the first kind
  We introduce an index of convergence for double sequences of real numbers. This index is used to describe the behaviour of some bivariate interpolation sequences at points of discontinuity of the first kind. We consider in particular the case of bivariate Lagrange and Shepard operators. 
Michele Campiti, Giusy Mazzone, Cristian Tacelli
math.FA