def mul(lhs: Any, rhs: Any, default: Any = RaiseTypeErrorIfNotProvided) -> Any:
    """Returns lhs * rhs, or else a default if the operator is not implemented.

    This method is mostly used by __pow__ methods trying to return
    NotImplemented instead of causing a TypeError.

    Args:
        lhs: Left hand side of the multiplication.
        rhs: Right hand side of the multiplication.
        default: Default value to return if the multiplication is not defined.
            If not default is specified, a type error is raised when the
            multiplication fails.

    Returns:
        The product of the two inputs, or else the default value if the product
        is not defined, or else raises a TypeError if no default is defined.

    Raises:
        TypeError:
            lhs doesn't have __mul__ or it returned NotImplemented
            AND lhs doesn't have __rmul__ or it returned NotImplemented
            AND a default value isn't specified.
    """
    # Use left-hand-side's __mul__.
    left_mul = getattr(lhs, '__mul__', None)
    result = NotImplemented if left_mul is None else left_mul(rhs)

    # Fallback to right-hand-side's __rmul__.
    if result is NotImplemented:
        right_mul = getattr(rhs, '__rmul__', None)
        result = NotImplemented if right_mul is None else right_mul(lhs)

    # Don't build up factors of 1.0 vs sympy Symbols.
    if lhs == 1 and is_parameterized(rhs):
        result = rhs
    if rhs == 1 and is_parameterized(lhs):
        result = lhs
    if lhs == -1 and is_parameterized(rhs):
        result = -rhs
    if rhs == -1 and is_parameterized(lhs):
        result = -lhs

    # Output.
    if result is not NotImplemented:
        return result
    if default is not RaiseTypeErrorIfNotProvided:
        return default
    raise TypeError(f"unsupported operand type(s) for *: '{type(lhs)}' and '{type(rhs)}'")
Returns lhs * rhs, or else a default if the operator is not implemented.

    This method is mostly used by __pow__ methods trying to return
    NotImplemented instead of causing a TypeError.

    Args:
        lhs: Left hand side of the multiplication.
        rhs: Right hand side of the multiplication.
        default: Default value to return if the multiplication is not defined.
            If not default is specified, a type error is raised when the
            multiplication fails.

    Returns:
        The product of the two inputs, or else the default value if the product
        is not defined, or else raises a TypeError if no default is defined.

    Raises:
        TypeError:
            lhs doesn't have __mul__ or it returned NotImplemented
            AND lhs doesn't have __rmul__ or it returned NotImplemented
            AND a default value isn't specified.
    
cirq-core/cirq/protocols/mul_protocol.py