For example

```
>>> x
tensor([[[[ 1., 3.],
[ 4., 6.]],
[[-1., -3.],
[-4., -7.]]]])
>>> x.mean([3, 0, 1])
tensor([ 0.0000, -0.2500])
>>> x.mean([3, 0])
tensor([[ 2.0000, 5.0000],
[-2.0000, -5.5000]])
>>> x.mean([3, 0]).mean([1])
tensor([ 3.5000, -3.7500])
```

I had believed that, doing mean([3, 0, 1]) is equivalent of doing x.mean([3, 0]).mean([1])