fact: Definition kfinite_subtype_singleton {X : UU} (x : X) : kfinite_subtype X.
imports: UniMath.Foundations.Propositions UniMath.MoreFoundations.PartA UniMath.MoreFoundations.Notations UniMath.Combinatorics.FiniteSets UniMath.Combinatorics.StandardFiniteSets UniMath.MoreFoundations.Subtypes UniMath.Combinatorics.KFiniteTypes