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Reference.org
Layered permutation
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<p>In the mathematics of <a href="/facts/Permutation/JSw9ukmv">permutations</a>, a layered permutation is a permutation that reverses contiguous blocks of elements. Equivalently, it is the <a href="/facts/Skew_and_direct_sums_of_permutations/HzheMwYt">direct sum</a> of decreasing permutations. </p><p>One of the earlier works establishing the significance of layered permutations was Bóna (1999), which established the <a href="/facts/Stanley%25E2%2580%2593Wilf_conjecture/pHDS7tHY">Stanley–Wilf conjecture</a> for classes of permutations forbidding a layered permutation, before the conjecture was proven more generally. </p>