I'm studying certain polynomials of 2 complex variables, say x and y. These polynomials have roots at the non-negative integers, that is both $x$ and $y$ have to be
$x,y \in \mathbb{N}$
simultaneously with the restriction that
$x+y \leq A$
for some non-negative integer A. I'd like to know the basis for these polynomials of minimal total degree (sum of degrees in $x$ and $y$), up to overal constants. I think this basis is:
$\left(x \atop n\right)\left(y \atop A+1-n\right)$
for integer $n$ with $0 \leq n \leq A+1$. The brackets are falling factorials:
$\left(x \atop n\right) = x (x-1)....(x-n-1)$
with $\left(x \atop 0\right)\equiv 1$
At the moment I have only a proof-by-lack-of-imagination argument that this is the full set. Of course, I'd also like to know how to generalize to multiple complex variables :)