Go backwards to a previous point in the trajectory. Useful to implement loops.
rollback(.trj, amount, times = 1, check)the trajectory object.
the amount of activities (of the same or parent trajectories) to roll back.
the number of repetitions until an arrival may continue.
a callable object (a function) which must return a boolean. If
present, the times parameter is ignored, and the activity uses this
function to check whether the rollback must be done or not.
Returns the trajectory object.