[gecode-users] Clockwise constraint

[Guido Tack]

Malcolm Ryan wrote:

> What I need is a reified version of the pairwise rel(). Then I could
> say:
>
> a < c --> a < b < c
> b < a --> b < c < a
> c < b --> c < a < b
>
> Since there is no value of 'a' that satisfies c < a < b, it would have
> to deduce that b < c.
>
> Representing this as (c < a) and (a < b) is not good enough, as there
> are possible values of 'a' to satisfy each of the inequalities
> individually, just not both together.

Oh, I somehow didn't see that it's always ternary!  In that case you  
might really want to try the extensional constraint.  Just implement a  
generator that lists all allowed tuples.

Cheers,
	Guido