@MartinSleziak, I don't think the software allows negative filters. Anyway, I see only 92 followers when I hover over this tag, which is low but is more than for the polynomials tag. So I agree it has positive utility to someone, even if its appearances have negative utility for me. —
Matt F. 2 hours ago
While studying the behaviour of umbilic points on Weingarten surfaces I discovered that the following combinatorial identity must be true.
For all $l,m\in{\mathbb N}$ with $l\geq m-1\geq0$ the following holds:
$
\sum_{k=m-1}^l(-1)^{k+m}\frac{k+2}{k+1}{l \choose k}{k+1 \choose m}=
\left\{\begin{...
