This utility function converts f to a multiset. A multiset is represented in the form ; it is a list of pairs where each  is a value (an expression), and  is its multiplicity (an integer).

If f is a table, each index is interpreted as a value and the associated entry (which should be an integer) is interpreted as its multiplicity.

If f is an algebraic expression, each factor is interpreted as a value, and the exponent to which this factor is raised (which should be an integer) is interpreted as its multiplicity.

If f is a list, the number of instances of each entry in the list is interpreted as its multiplicity.