I'm currently reading the paper "Higher Spin extension of cosmological spacetimes in 3d: asymptotically flat behaviour with chemical potentials in thermodynamics" I'm looking at equation (3) on page 4. I know that symmetrization brackets work like this A_(a b) = (A_ab + A_ba)/2. However I have never seen the expression given for [J_ab, J_cd] with the two brackets. How should one interpret this? Furthermore: Does anyone know a site where one can look up representations of Lie algebras? I'm specifically looking for a representation of this algebra (isl(3,R)) Thanks so much in advance!