numelems( M ) returns the number of elements of the MultiSet M, counted by multiplicity.

$M≔\mathrm{MultiSet}\left(a=2\,b=5\right)$

$M≔\left\{\left[a\,2\right]\,\left[b\,5\right]\right\}$

$\mathrm{numelems}\left(M\right)$

$7$

The MultiSet/numelems command was introduced in Maple 2016.

For more information on Maple 2016 changes, see Updates in Maple 2016.