d=[[1,2,3],[4,5,6],[7,8,9],[2,4,6],[1,3,7]];
 q=[];
 f(c)=(
     c<=2? return(c)
         : (
             q=pop(d);
             c=c-1;
             continue();
           )
 );
 f(4);
 
 -> 2