**Tensor[Any, ...]**

Ah, I'd missed Guido's comment that this is not valid syntax. Damn.

`Tensor[*Tuple[Any, ...]]` is certainly one option, but for the reasons in the previous section I don't like that it forces us into allowing unboundedness.

Could we perhaps just say that an unparameterized `Tensor` *behaves* as if it were `Tensor[Any, ...]` despite this not being valid syntax? How ugly a special-case would it be?

**Arbitrary-rank tensors**

Oh, man, super well-caught! You're right, committing to invariance by default does put us in a tricky situation.

But then - trying this with a regular `TypeVar`, mypy seems to be happy with the following:

```

from typing import Generic, TypeVar

T = TypeVar('T')

class Tensor(Generic[T]):

    pass

def expects_arbitrary_tensor(x: Tensor):

    pass

def expects_concrete_tensor(x: Tensor[int]):

    pass

x: Tensor = Tensor()

expects_concrete_tensor(x)

y: Tensor[int] = Tensor()

expects_arbitrary_tensor(y)

```

Any idea why that works?