What is the meaning of `None`

indices as arguments to core ATen’s `aten.index`

, which has type signature:

```
index.Tensor(Tensor self, Tensor?[] indices) -> Tensor
```

One guess is that a `None`

index stands for the entire corresponding dimension: e.g. if `v`

is a tensor with shape `[2, 3]`

, then `index(v, [None, tensor([0, 1])])`

is equivalent to `index(v, [tensor([0, 1]), tensor([0, 1])])`

. However, this is not the case as shown by the example below:

```
>>> v
tensor([[0.1824, 0.1772, 0.6883],
[0.5761, 0.7300, 0.0843]])
>>> torch.ops.aten.index(v, [torch.tensor([0, 1]), torch.tensor([0, 1])])
tensor([0.1824, 0.7300])
>>> torch.ops.aten.index(v, [None, torch.tensor([0, 1])])
tensor([[0.1824, 0.1772],
[0.5761, 0.7300]])
```