Before revision:  To remove those critical values of \Delta t, we propose a slight modification of the original LF-LTS method which nonetheless preserves its desirable properties: it is fully explicit, second-order accurate, satisfies a three-term (leapfrog like) recurrence relation, and conserves the energy.
After revision:  To remove those critical values of \Delta t, we apply a slight modification of the original LF-LTS method which nonetheless preserves its desirable properties: it is fully explicit, second-order accurate, satisfies a three-term (leapfrog like) recurrence relation, and conserves the energy.