The multiplicity of an element in a multiset is simply the number of times that the element
occurs in the multiset. For example, in the multiset $\{-2, 1, \pi, 1, 3.4, -2, -2\}$, the
multiplicity of $\pi$ is 1, the multiplicity of $1$ is 2, and the multiplicity of $-2$ is 3.
