Three examples of join computations

This article answers three questions of J. Almeida. Using combinatorial, algebraic and topological methods, we compute joins involving the pseudovariety of finite groups, the pseudovariety of semigroups in which each idempotent is a right zero and the pseudovariety generated by monoids M such that each idempotent of M\{1} is a left zero.ESPRIT - BRA Working Group 6317 Asmics-2.Project de Recherche Coordonnée "Mathématique et Informatique".Junta Nacional de Investigação Científica e Tecnológica (JNICT) - Projecto SAL (PBIC/C/CEN/1021/92)