See ``PlaceholderType.resolve``

def resolve(self, other: Type) -> Optional[Type]:
        """See ``PlaceholderType.resolve``"""
        if not isinstance(other, NltkComplexType):
            return None
        expected_second = ComplexType(NUMBER_TYPE,
                                      ComplexType(ANY_TYPE, ComplexType(ComplexType(ANY_TYPE, ANY_TYPE),
                                                                        ANY_TYPE)))
        resolved_second = other.second.resolve(expected_second)
        if resolved_second is None:
            return None

        # The lambda function that we use inside the argmax  must take either a number or a date as
        # an argument.
        lambda_arg_type = other.second.second.second.first.first
        if lambda_arg_type.resolve(NUMBER_TYPE) is None and lambda_arg_type.resolve(DATE_TYPE) is None:
            return None

        try:
            # This is the first #1 in the type signature above.
            selector_function_type = resolved_second.second.first
            # This is the second #1 in the type signature above.
            quant_function_argument_type = resolved_second.second.second.first.second
            # This is the third #1 in the type signature above.
            return_type = resolved_second.second.second.second

            # All three placeholder (ph) types above should resolve against each other.
            resolved_first_ph = selector_function_type.resolve(quant_function_argument_type)
            resolved_first_ph.resolve(return_type)

            resolved_second_ph = quant_function_argument_type.resolve(resolved_first_ph)
            resolved_second_ph.resolve(return_type)

            resolved_third_ph = return_type.resolve(resolved_first_ph)
            resolved_third_ph = return_type.resolve(resolved_second_ph)

            if not resolved_first_ph or not resolved_second_ph or not resolved_third_ph:
                return None

            return ArgExtremeType(resolved_first_ph, lambda_arg_type)
        except AttributeError:
            return None