fact: Definition indexed_carrier_to_carrier_union {X I : UU} (index : I → hsubtype X) : (∑ (i : I), (carrier (index i))) → (carrier (⋃ index)).
imports: UniMath.Foundations.Propositions UniMath.MoreFoundations.PartA UniMath.MoreFoundations.Notations UniMath.Combinatorics.FiniteSets UniMath.Combinatorics.StandardFiniteSets UniMath.MoreFoundations.Subtypes UniMath.Combinatorics.KFiniteTypes