3 problems

Let $(A,S)$ be a Birkhoff interpolation scheme, with $S$ a lower set, and fix non-negative integers $p$ and $q$. An inverse shift moves elements of $A$ downwards and to the left wi…

Let $(A,S)$ be a Birkhoff interpolation scheme, where $A$ is a finite set of derivative indices and $S$ is a lower set. Fix non-negative integers $p$ and $q$, and let $(p,q)$-recta…

A lower set $S$ is a finite subset of the non-negative integer lattice such that, whenever $(\beta_1,\beta_2)\in S$ and $0\leq\alpha_i\leq\beta_i$ for $i=1,2$, one has…