Solution (source code)

= Solution

For <events> $A,B$ with $\mathbb P(B)>0$, the <conditional probability> is
$$
\boxed{\mathbb P(A\mid B)=\frac{\mathbb P(A\cap B)}{\mathbb P(B)}.}
$$
It measures the <probability> of $A$ after restricting the <sample space> to $B$ and renormalizing. This quotient does not define <conditional probability> given an <event> of zero <probability>.