MathOverflow

Suppose you in a more comprehensive framework has the result that U is the least set such that all axioms of NBG-- (NBG, minus extensionality and regularity), hold; replacement is here, as expected, obtained relative to the least class containing U and...

Given a graph $G = (V,E)$, a vertex-deleted subgraph of $G$ is a subgraph formed by deleting exactly one vertex from $G$.
For a graph $G$, the deck of $G$, denoted $D(G)$, is the multiset of isomorphism classes of all vertex-deleted subgraphs of $G$. Each graph in $D(G)$ is called a card. Two graphs that have the same deck are said to be hypomorphic....

Let $X,Y,Z$ be smooth varieties and assume that $X,Y$ are closed subvarieties of $Z$. Suppose that $\mathrm{codim}_Y X \cap Y = \mathrm{codim}_Z X$. Then is it true that $X \cap Y$ is a classical (as opposed to derived) intersection? If this fact is...

Let
$T(n,k)$ be A126347, i.e., an integer coefficients with row polynomials $B(n,x)$ such that $$ B(n,x) = \sum\limits_{k=0}^{n-1} \binom{n-1}{k} B(k,x) x^k, \\ B(0,x) = 1. $$
$R(n,k,x)$ be the family of polynomials such that $$ R(n,k,x) = R(n-1,n-1,x) + x^n \sum\limits_{j=0}^{k-1} R(n-1,j,x), \\ R(0,0,x) = 1. $$...