Sorry to be so late to the conversation but can someone point me to a discussion of why `TypeGaurd[T]` is not a subtype of bool?

It seems a bit strange to not be able to pass a type guard as a filter e.g.:
```
def filter(f: Callable[[object], bool], xs: Sequence[object]) -> Sequence[object]: ...

def is_int(x: object) -> TypeGaurd[int]: ...

filter(is_int, [...]) # error?
```