class _DelegatorMixin():
    # this method signature is unchanged
    def get_verification_result(
        self,
        delegated_role: str,
        payload: bytes,
        signatures: Dict[str, Signature],
    ) -> VerificationResult

class Root():
    # new method to get a combined verification result from two roles (self and other) 
    def get_root_verification_result(
        self,
        other: Root,
        payload: bytes,
        signatures: Dict[str, Signature],
    ) -> RootVerificationResult
        # build a RootVerificationResult using self.get_verification_result()
        # and other.get_verification_result()

@dataclass
class VerificationResult:
    # New field threshold, modified type of signed and unsigned
    verified: bool
    threshold: int
    signed: Dict[str, Key]
    unsigned: Dict[str, Key]
 
    def __bool__(self) -> bool:
        return self.verified

@dataclass
class RootVerificationResult:
    # This dataclass operates like a VerificationResult except:
    # * No threshold
    # * you can access underlying VerificationResults if you need to

    results: tuple[VerificationResult, VerificationResult]

    def __bool__(self) -> bool:
        return self.verified

    @property
    def verified(self) -> bool:
        return self.results[0].verified and self.results[1].verified 
    
    @property
    def signed(self) -> dict[str, Key]:
        # return a "union" of both results[0].signed and results[1].signed

    @property
    def unsigned(self) -> dict[str, Key]:
        # return a "union" of both results[0].unsigned and results[1].unsigned