MathOverflow

A cardinal is Reinhardt if $\kappa$ is the critical point of a nontrivial elementary embedding of $V$ to itself, where $V$ is the class of all sets. As Reinhardt cardinals are inconsistent with $\mathrm{ZFC}$, work in $\mathrm{ZF}j$, which is $\mathrm...

Let $\mathbb{P}_{a, q}$ denote the set of primes congruent to $a$ modulo $q$. Are there any estimates for the number of $3$-Arithmetic Progressions in the set $\mathbb{P}_{a, q}\cap [1, X]$, where $(a, q) = 1$? For $q$ at most a constant, such an estimate...

Here's a problem;
A question-and-answer game establishes the scores obtained as follows:
For 1 correct answer, the number of points obtained x equals +1.

Here is a sequence of polynoms - (presumably) counting N-tuples of ANTI-commuting 2x2 matrices over $F_p, p>2$. (That is just the case of 2x2 matrices, and (surprisingly) it is not so easy to see a pattern ! Compare to commuting matrices where pattern...