es by other unused axes.

>>> A = coo_array(np.arange(3*4*5*6)).reshape((3,4,5,6))
>>> B = coo_array(np.arange(3*4*5*6)).reshape((5,4,6,3))
>>> A.dot(B).shape
(3, 4, 5, 5, 4, 3)
r