## Leapfrog is time reversible because of the symmetric way in which it is defined, unlike the other schemes.

- In Euler, forward and backward steps do not cancel since they use different derivatives at different times.
- In Midpoint, the estimate of the derivative is based on an extrapolation from the
*left-hand*side of the interval. On time reversal, the estimate would be based on the*right-hand*side, not the same. - Similarly, RK4 is not time reversible.