generic super false-posistive error on argument type

input:

NT = TypeVar('NT', int, float)
NTU = Union['KspVar[NT]', 'AstBase[NT]', 'ProcessNum[NT]', NT]


class AstOperatorUnary(AstBase[NT], ProcessNum[NT]):
    arg1: NTU[NT]
    string: ClassVar[str]
    priority: ClassVar[int]

    def __init__(self, arg1: NTU[NT]) -> None:
        self.arg1: NTU[NT] = arg1
        self.arg1_pure: NT = get_value(arg1)
        self.arg1_str: str = get_compiled(arg1)


class AstOperatorDouble(AstOperatorUnary[NT]):
    arg2: NTU[NT]

    def __init__(self, arg1: NTU[NT], arg2: NTU[NT]) -> None:
        super().__init__(arg1)
        self.arg2 = arg2
        self.arg2_pure: NT = get_value(arg2)
        self.arg2_str: str = get_compiled(arg2)

Traceback:

E:\packages\pyksp\pyksp\new_base_types.py:285: error: Argument 1 to "__init__" of "AstOperatorUnary" has incompatible type "Union[KspVar[int], AstBase[int], ProcessNum[int], int]"; expected "Union[KspVar[NT], AstBase[NT], ProcessNum[NT], NT]"
E:\packages\pyksp\pyksp\new_base_types.py:285: error: Argument 1 to "__init__" of "AstOperatorUnary" has incompatible type "Union[KspVar[float], AstBase[float], ProcessNum[float], float]"; expected "Union[KspVar[NT], AstBase[NT], ProcessNum[NT], NT]"

ProcessNum has not got __init__

Start with the generic class definitions in pyksp/new_base_types.py around line 285 and reproduce the reported mypy errors using the provided AstOperatorUnary and AstOperatorDouble example. Investigate why the super().init call rejects the specialized union; done means the false-positive argument errors no longer occur for this case.