%include "y12.m"
x1 = [x:y:[]|x,y<-[1..4]]
   ||-> [[1,1],[1,2],[1,3],[1,4],[2,1],[2,2],[2,3],[2,4],[3,1],[3,2],[3,3],[3,4],[4,1],[4,2],[4,3],[4,4]]
x2 = [x:y:[]//x,y<-[1..4]]
   ||-> [[1,1],[1,2],[2,1],[1,3],[2,2],[3,1],[1,4],[2,3],[3,2],[4,1],[2,4],[3,3],[4,2],[3,4],[4,3],[4,4]]