Commute 3 partial derivatives

[Asanka Amarasinghe]

I have a question regarding parallel derivatives in xCoba. Once I found components program cannot identify, for example, PDB[{3,-B}][PDB[{1,-B}][PDB[{2,-B}][A[{1,-B},{1,-B}]]]] is the same as PDB[{2,-B}][ PDB[{3,-B}][[PDB[{1,-B}][A[{1,-B},{1,-B}]]]. and so it will not simplify. further

I use 

W[-Mu, -Nu] ==  some expression with PDBs

ToBasis[B] /@ %;

ToBasis[B] /@ %;

% /. CD -> PDB;

TraceBasisDummy /@ %;

Flatten@ToValues@ComponentArray[%];

% /. Equal -> ComponentValue

Can someone please help me with this issue.