“…Let {B α (x, y), α ∈ F }, F ⊂ Z 2 , be an appropriate set of bivariate B-spline functions spanning a space of bivariate splines of degree ρ defined on a uniform triangulation of Ω ′ of mesh size h > 0, and let {B α (z), α ∈F },F ⊂ Z, be an appropriate set of B-spline functions in one dimension, spanning a space of splines of degreē ρ defined on a uniform partition of Ω ′′ of step-length h. We consider bivariate and univariate quasi-interpolants (see e.g. de Boor 2001, Chap.12, Lyche andSchumaker 1975, for the univariate case and de Boor et al 1993, Chap.3, for the bivariate case), P f (x, y) andP f (z), of the form…”