This paper is most likely the last mathematical article published by the late M.-P. Schützenberger, who died in July 1996. It was writen in view of the celebration of André Lentin's jubilee, held in February 1996. M.-P. Schützenberger, actually too sick, did not attend that scientific meeting. But he had the will despite distressing suffering, to prepare the present work and to offer it to his friend : and dit it. He expressed to us his satisfaction to know that this work would be published in "Mathématique, Informatique et Sciences humaines". Here it is.
展开▼
