Commutator algebra could be improved

[bjodah]

From http://stackoverflow.com/questions/36095622

from sympy.physics.quantum import Commutator as Comm
from sympy.physics.quantum import Operator
A = Operator('A')
B = Operator('B')
C = Comm(Comm(Comm(A,B),A),B)
D = Comm(Comm(Comm(A,B),B),A)
E = (C-D).expand(commutator=true)
E

where the expected output would be 0 but it is:

[[[A,B],A],B] - [[[A,B],B],A]

one can invoke the .doit() method:

>>> simplify(E.doit())
0

but arguably Commutator._eval_expand_commutator should already know this identity.