MathOverflow

The standard Gale-Ryser theorem is for the existence of a $(0,1)$-matrix given exact row sums $R = (r_1, \dots, r_K)$ and exact column sums $C = (c_1, \dots, c_M)$. What if we relax the column sums and want at most those $c_j$ instead of exactly those...

Let $G$ be a hereditary and closed set of $2^{\Bbb N}$. And let $G^\max$ be the set of maximals of $G$ with inclusion. This set is $G_\delta$ in $2^{\Bbb N}$. That means I can see it as a closed set of the Baire space $\Bbb{N^N}$, that is, as $[T]$ for...

One of the strongest results on the decidability of theories is Rabin's Tree Theorem. One way to state it is the following: tThe problem of deciding whether a sentence on the monadic second order (MSO) theory of graphs has finite tree model is decidable...

I was reading the proof of Milne étale cohomology on Brauer groups IV.2.1. Prove that if $A\otimes k(x)$ is a central simple algebra over $k(x)$ for all $x$. Then there exists (finite) etale covering $(U_i)$ such that $A|_{U_i}\cong M_{n_i}(U_i)$ for...