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10 votes
3 answers
1k views

What's the number of solutions of the quadratic equation $x_1^2+\dots+x_m^2=0$ over finite ring $\mathbb{Z}/p^n$?

I want to calculate the number of solutions to the quadratic equation $$x_1^2+\dots+x_m^2=0$$ where $m$ is odd (a given number) and $x_i\in\mathbb{Z}/p^n$ for a given prime number $p$ and a given ...
0 votes
0 answers
257 views

How to prove the map of rings $\mathcal{R} \to \mathcal{R'}$ is flat?

We fix a finite extension $K$ of $p$-adic field $\mathbb{Q}_p$ with ring of integers $\mathcal{O}_K$ and residue field $\kappa$. Consider the ring of witt vectors $W(\kappa)$ over the residue field $\...
4 votes
0 answers
144 views

Does a countably generated $\mathbb{Q}$-algebra inject into some $p$-adic field?

Let $K$ be a subfield of $\mathbb{C}$. If $K$ is finitely generated over $\mathbb{Q}$, then $K$ injects into $\mathbb{Q}_p$ for some $p$. Assume that $K$ is countably generated, i.e., $K= \...