Invariance identity for a cubic trace tensor (source code)

= Invariance identity for a cubic trace tensor

The <trace> of a <commutator> gives
$$
B([W,X],Y,Z)+B(X,[W,Y],Z)+B(X,Y,[W,Z])=0.
$$
In a basis, cyclicity converts this to $c_{da}{}^\ell B_{bc\ell}+c_{db}{}^\ell B_{ca\ell}+c_{dc}{}^\ell B_{ab\ell}=0$.

// Target: lie-theory.bigb