fact: Definition isAssociative_seq := ∏ (x : Sequence (Sequence X)), iterop_seq (FiniteSequences.flatten x) = iterop_seq_seq x.
imports: UniMath.Combinatorics.Lists UniMath.Combinatorics.FiniteSequences UniMath.Algebra.RigsAndRings UniMath.Foundations.UnivalenceAxiom UniMath.MoreFoundations.Tactics UniMath.Algebra.Groups UniMath.MoreFoundations.NegativePropositions