Naïve set theory MOC Multiset A multiset is a generalization of a set which may contain the same element more than once, set where we write for the underlying set. This may be formalized as as a set with a generalized characteristic function so that is the multiplicity of in as a set with an equivalence relation , such that and . In these notes, we will write for the multiset related to an ordered tuple . When it is clear, I may use to refer to . tidy | en | sembr