Formulate the following problem using appropriate global constraints
(alldiff, cardinality, nvalues, stretchCycle) and channeling 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. Hints. Let wsd be the guard at station s on night d, and let
yid be the station assigned to guard i on night d. Because two guards are
unassigned on a given night, two dummy stations are necessary to make the
channeling constraints work.