fact: Definition path_sum {A B : Type} (z z' : A + B) (pq : match z, z' with | inl z0, inl z'0 => z0 = z'0 | inr z0, inr z'0 => z0 = z'0 | _, _ => Empty end) : z = z'.
imports: HoTT.Basics Types.Empty Types.Unit Types.Prod Types.Sigma Types.Bool Types.Forall