Transitive Hall sets
  We give the definition of Lazard and Hall sets in the context of transitive factorizations of free monoids. The equivalence of the two properties is proved. This allows to build new effective bases of free partially commutative Lie algebras. The commutation graphs for which such sets exist are completely characterized and we explicit, in this context, the classical PBW rewriting process. 
G\'erard Henry Edmond Duchamp (LIPN), Jean-Gabriel Luque (IGM),   Marianne Deboysson-Flouret (LIH)