Riemann Simplification issue

[Sergio González]

Hi everyone,

I have an issue with Simplification that I hope you could clear.

By contracting RiemannCD[a,m,n,p] with the identity RiemannCD[b,-m,-n,-p]+RiemannCD[b,-n,-p,-m]+RiemannCD[b,-p,-m,-n]=0 it is easy to prove that RiemannCD[a,m,n,p] RiemannCD[b,-m,-n,-p]=  2RiemannCD[a,m,n,p] RiemannCD[b,-n,-m,-p]

As it is due to Bianchi identity, Simplification or FullSimplification acting on RiemannCD[a,m,n,p] RiemannCD[b,-m,-n,-p] - 2RiemannCD[a,m,n,p] RiemannCD[b,-n,-m,-p] should return zero but it is not.

I am not sure if it is not programmed and I should make an automatic rule or if there is some other instruction that I could use in order to simplify this expression. 

Hope you can help me.