Appears in collection : Combinatorics and Arithmetic for Physics : Special Days

Elimination of generators (commutative or noncommutative) is linked to many combinatorial theories (Bisection and codes, Semidirect products of pre- sented groups and Lie algebras, Strange gradings over semigroups, Lazard elim- ination). We will describe unifying (categorical) links between some of these theories and give general results allowing to get semidirect decompositions at first sight. (Joint work with Paul-André Melliès and Vu Nguyen Dinh.)