Yann H. Péresse

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Let ΩΩ be the semigroup of all mappings of a countably infinite set Ω. If U and V are subsemigroups of ΩΩ, then we write U ≈ V if there exists a finite subset F of ΩΩ such that the subgroup generated by U and F equals that generated by V and F . The relative rank of U in ΩΩ is the least cardinality of a subset A of ΩΩ such that the union of U and A(More)
Though still a relatively young subject within discrete mathematics, the study of pattern classes of permutations is one of the fastest growing and is useful in theoretical computer science as well as various areas of mathematics. There are two commonly used forms of notation for permutations: a1a2 . . . an denotes the permutation which sends i to ai for i(More)
In this paper, we consider the group Aut(Q,≤) of order-automorphisms of the rational numbers, proving a result analogous to a theorem of Galvin’s for the symmetric group. In an announcement, Khélif states that every countable subset of Aut(Q,≤) is contained in an N-generated subgroup of Aut(Q,≤) for some fixed N ∈ N. We show that the least such N is 2.(More)
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