Formulate the following problem using the appropriate global constraints.
There are six security guards and four stations.
Each station must be staffed by exactly one guard each night of the week.
A guard must be on duty four or five nights a week.
No station should be staffed by more than three different guards during the week.
A guard must never staff the same station two or more nights in a row and must staff at least three different stations during the week.
A guard must not staff Stations 1 and 2 on consecutive nights (in either order), and similarly for Stations 3 and 4. Every week will have the same schedule.