 This work is sometimes regarded as one of the precursors of the celebrated AdS/CFT correspondence.Henneaux also studied the geometrical and algebraic aspects of theories with a gauge freedom, and in particular on the so-called Becchi-Rouet-Stora-Tyutin symmetry and its cohomology.More recently, in collaboration with Thibault Damour, he showed that hyperbolic Coxeter groups appear somewhat unexpectedly in gravitational theories and their supersymmetric extensions, in the BKL behaviour of the fields near a spacelike singularity.