Discriminant of a quaternion algebra (reviewed)

Let $B$ be a quaternion algebra over $\Q$. We say that $B$ is ramified at a prime $p$ if $B\otimes_{\Q} \Q_p$ is a division algebra over $\Q_p$; otherwise, we say that $B$ is split at $p$.

The discriminant $\operatorname{disc}(B)$ of $B$ is the product of primes $p$ at which $B$ is ramified.