On certain multivariate Vandermonde determinants whose variables separate

We prove that for almost square tensor product grids and certain sets of bivariate polynomials the Vandermonde determinant can be factored into a product of univariate Vandermonde determinants. This result generalizes the conjecture [Lemma 1, L. Bos et al. (2009), Dolomites Research Notes on Approximation, 2:1-15]. As a special case, we apply the result to Padua and Padua-like points.