def _parameter_names_(self) -> AbstractSet[str]:
        """Returns a collection of string names of parameters that require
        resolution. If _is_parameterized_ is False, the collection is empty.
        The converse is not necessarily true, because some objects may report
        that they are parameterized when they contain symbolic constants which
        need to be evaluated, but no free symbols.
        """
Returns a collection of string names of parameters that require
        resolution. If _is_parameterized_ is False, the collection is empty.
        The converse is not necessarily true, because some objects may report
        that they are parameterized when they contain symbolic constants which
        need to be evaluated, but no free symbols.
        
cirq-core/cirq/protocols/resolve_parameters.py