... there exists π∈ Xwhich is a deflation of π by permutations in Y . The proof of Lemma 3.1 then tells usthat πY≤ π, completing the proof.Any expression of the form π = πY[α1, . . . , αk] ... avoidthe permutation 321 and so the antichain in the proof of Theorem 6.1 lies in thebasis of Av(25134) Y in both cases.(ii) All of the classes of the form Y = Av(α, β) where (α, β) is (4321, 4312), ... profile of 3415672 is 3142 because of the segments 34, 1, 567 and 2.The notion of a “Y -profile” connects this idea with the definition of the substitutiondecomposition π = σ[π1, . . . , πm] of...