Slicing syntax question

[metulburr]

>>> import numpy as np
>>> a = np.arange(12).reshape(3,4)
>>> a
array([[ 0,  1,  2,  3],
       [ 4,  5,  6,  7],
       [ 8,  9, 10, 11]])
>>> a[:,[1,2,3]]
array([[ 1,  2,  3],
       [ 5,  6,  7],
       [ 9, 10, 11]])
>>> a[:, [1,3]]
array([[ 1,  3],
       [ 5,  7],
       [ 9, 11]])