<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def verify_header(self, key, val):
 """ Check that a particular header claim is present and has a specific value :param key: The claim :param val: The value of the claim :raises: KeyError if the claim is not present in the header :return: True if the claim exists in the header and has the prescribed value """


        if isinstance(val, list):
            if self.headers[key] in val:
                return True
            else:
                return False
        else:
            if self.headers[key] == val:
                return True
            else:
                return False