[eclipse-clp-users] Problem formulating simple ic_sets test

I'm new to ECLiPSe, and I'm trying simple tests to acquaint myself with
its features. In this test, I'm experimenting with a variable representing
a member of a finite set. My understanding is that I should be able to
define the set, then create a variable representing a member, and then use
that variable to reduce the size of the search space for a query (compared
to using a simple variable and then testing the variable after it's
bound).

In this test, I expected to limit the search for my atLoc/3 query to just
those atLoc clauses whose 3rd arg is in the set {1917,1918,1919}.

Why does the query fail?


?- lib(ic_sets), assert(atLoc(blueObj, 32, 1918)), TargetObjPos :: [] ..
[1917, 1918, 1919], atLoc(TargetObjId, EndingFrameId, TargetObjPos).
No