fact: Definition upto' {X:hSet} {C:WOSubset X} (c:C) : proper_subtypes_set X.
imports: UniMath.MoreFoundations.DecidablePropositions UniMath.MoreFoundations.Propositions UniMath.MoreFoundations.Subtypes UniMath.MoreFoundations.Sets UniMath.MoreFoundations.AxiomOfChoice UniMath.Combinatorics.OrderedSets