Generalized Shubnikov space groups.
Let be a unitary space. For an arbitrary subgroup of the full symmetric group and an arbitrary irreducible unitary representation of , we study the generalized symmetry class of tensors over associated with and . Some important properties of this vector space are investigated.
Un système fini d’isométries partielles de est dit à générateurs indépendants si les composés non triviaux fixent au plus un point. On décrit un procédé simple et naturel pour obtenir des générateurs indépendants, sans modifier les orbites, pour tout système sans composante minimale homogène : en prenant la restriction de chaque générateur à un certain sous-intervalle de son domaine. Un système avec une composante minimale homogène ne possède pas de générateurs indépendants.
We prove that any countable set of surjective functions on an infinite set of cardinality ℵₙ with n ∈ ℕ can be generated by at most n²/2 + 9n/2 + 7 surjective functions of the same set; and there exist n²/2 + 9n/2 + 7 surjective functions that cannot be generated by any smaller number of surjections. We also present several analogous results for other classical infinite transformation semigroups such as the injective functions, the Baer-Levi semigroups, and the Schützenberger monoids.
A method of generating a practically unlimited number of quasigroups of a (theoretically) arbitrary order using the computer algebra system Maple 7 is presented. This problem is crucial to cryptography and its solution permits to implement practical quasigroup-based endomorphic cryptosystems. The order of a quasigroup usually equals the number of characters of the alphabet used for recording both the plaintext and the ciphertext. From the practical viewpoint, the most important quasigroups are of...
We give an algebraic proof of the fact that a generating set of the mapping class group Mg,1 (g ≥ 3) may be obtained by replicating a generating set of M2,1.
We study the generation of finite groups by nilpotent subgroups and in particular we investigate the structure of groups which cannot be generated by nilpotent subgroups and such that every proper quotient can be generated by nilpotent subgroups. We obtain some results about the structure of these groups and a lower bound for their orders.