fact: Definition clean_sum {X Y Z} (f : X -> Y + Z) : (forall x y, f x <> inl y) -> forall x, { z | inr z = f x }.
imports: HoTT(TruncType ExcludedMiddle abstract_algebra) HoTT(PropResizing.PropResizing) HoTT(Spaces.Nat.Core Spaces.Card) HoTT(Equiv.BiInv) HoTT(HIT.unique_choice) HoTT.Sets(Ordinals Hartogs Powers GCH AC)