def METHOD_NAME(self) -> bool:
    """
    Validate the signatures in the transaction.
    return: True if the transaction is valid, False otherwise
    """
    if self.signature_a != EMPTY_SIGNATURE:
        # Verify signature A
        pck = self.pack(signature_a=False, signature_b=False)
        valid_signature = default_eccrypto.is_valid_signature(
            default_eccrypto.key_from_public_bin(self.public_key_a), pck, self.signature_a)
        if not valid_signature:
            return False
    if self.signature_b != EMPTY_SIGNATURE:
        # Verify signature B
        pck = self.pack(signature_b=False)
        valid_signature = default_eccrypto.is_valid_signature(
            default_eccrypto.key_from_public_bin(self.public_key_b), pck, self.signature_b)
        if not valid_signature:
            return False
    if self.sequence_number < 1:
        return False
    return True