def all_measurement_key_names(self) -> frozenset[str]:
        """Returns the set of all measurement key names in this circuit.

        Returns: frozenset of strings that are the measurement key
            names in this circuit.
        """
        return frozenset(
            key for op in self.all_operations() for key in protocols.measurement_key_names(op)
        )
Returns the set of all measurement key names in this circuit.

        Returns: frozenset of strings that are the measurement key
            names in this circuit.
        
cirq-core/cirq/circuits/circuit.py