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One basic activity in combinatorics is to establish combinatorial identities by so-called ‘bijective proofs,’ which amounts to constructing explicit bijections between two types of the combinatorial objects in question. The aim of this paper is to show how techniques from the formal logic world can be applied directly to such problems studied completely independently in the world of combinatorics...
We provide a bijection between the permutations in Sn that avoid 3412 and contain exactly one 321 pattern with the permutations in Sn+1 that avoid 321 and contain exactly one 3412 pattern. The enumeration of these classes is obtained from their classification via reduced decompositions. The results are extended to involutions in the above pattern classes using reduced decompositions reproducing...
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