This is very clever. I'm a card magician and I don't think I've ever seen this one. I'm going to take a stab at explaining the math. A spectator removes N cards from a packet of 26 (Packet 1). This leaves 26-N in Packet 1. And N cards off to the side. A card is chosen from the other packet of 26 (Packet 2) placed on Packet 1 and covered with Pacet 2. This puts the chosen card 26 from the top of the new packet (Packet 3) Below the chosen card are 26-N cards. The special shuffle removes one card from above the chosen card for each card below the chosen card. This means we are subtracting 26-N from 26. 26- (26-N)=26-26+N=N So the chosen card ends up at N from the top which is the number of cards the spectator first cut off. Kind of confusing I know. Try doing the trick but putting the chosen card face up. You can then track what is happening during the special shuffle.
