By back to back, do you mean nurse 3 works shift 2 day 1 and shift 0 day 2? Or that nurse 3 always works two days in a row in the listed solutions? The example

By back to back, do you mean nurse 3 works shift 2 day 1 and shift 0 day 2? Or that nurse 3 always works two days in a row in the listed solutions? The example doesn't mention back to back shifts, only that a nurse can at most work one shift a day which in turn implies the constraint that no nurse can work shifts back to back (in the same day). One could easily add the constraint that a nurse scheduled on shift 2 cannot work shift 0 the next day.