// Tower of Hanoi Puzzle

// Rules
hanoi(return, source, target, aux) >< (int n)
| n==0 => 
          // Erase the source, target and aux
          source ~ Eraser,
          target ~ Eraser,
          aux ~ Eraser,

          // result
          return~[]

| _    => 
          // Duplicate the source, target and aux
	  source ~ Dup(src1, Dup(src2, src3)),
          target ~ Dup(tgt1, Dup(tgt2, tgt3)),
          aux ~ Dup(aux1, aux2),

          // recursive applications
          hanoi(ret1, src1, aux1, tgt1)~(n-1),
          hanoi(ret2, aux2, tgt2, src2)~(n-1),

          // result
          return << Append(ret1, (n,src3,tgt3):ret2);


// Net
hanoi(result, A, C, B) ~ 3;
result; // should be [(1,A,C),(2,A,B),(1,C,B),(3,A,C),(1,B,A),(2,B,C),(1,A,C)]