I think X-Y-Z is the sequence 1x-1y-1z where 1Z is a suit, then 2 ♣becomes puppet to 2♦ and 2♦ becomes GF, f.ex: 1♦-1♥ 1♠-2♦ (GF) While the sequence that is posted is x-y NT, though it works the same. 1x-1y 1NT- 2♣ is puppet to 2♦ either to play 2♦ or to come back with an invite. 2♦ is any GF. 2NT is transfer to 3♣ So f.ex : 1♦-1♠ 1NT-2♣ 2♦-2NT would be invitational with bal hand. I don't quite know what the sequence you posted means, but could it be something like invite with 5♠ and 4♦? Would think a bal hand with 4♠ and 4♦ would invite via 2NT.