fact: Fixpoint list_to_set_disj `{SingletonMS A C, Empty C, DisjUnion C} (l : list A) : C := match l with [] => ∅ | x :: l => {[+ x +]} ⊎ list_to_set_disj l end.
imports: Coq(Permutation) Coq.ssr((notations) ssrfun) stdpp(options)