  Out-of-time-order correlators are widely used as an indicator of quantum
chaos, but give false-positive quantum Lyapunov exponents for integrable
systems with isolated saddle points. We propose an alternative indicator that
fixes this drawback and retains all advantages of out-of-time-order
correlators. In particular, the new indicator correctly predicts the average
Lyapunov exponent and the Ehrenfest time in the semiclassical limit, can be
calculated analytically using the replica trick, and satisfies the bound on
chaos.
