regarding "card trick without trick"
There is a better solution for the question if the card design is not symmetric along the horizontal or vertical split( OR it is not required that all cards be given face down).

 *  > top side
 
 
  > bottom side

A card can be arranged in two positions:
top side up (Or face up), and
top side down (Or face down)
As usual, one card is for specifying the suit.
But we can use all the 4 cards for specifying the number from 1 to 13.
We can arrange the cards (up or down. "up" corresponds to binary 1 and "down" to binary 0.
So the 1st card provides two units of information:
1. the suit of the card, and
2. the MSB of the binary number.
the rest of the three cards give the rest of the digits of the binary number.
Rakesh
Sunday, March 30, 2003
In general, only certain cards (only oddnumbered nonface cards that are not diamonds, I believe) are asymmetric in that way. Though you can get trick decks where the backs are subly different after rotation.
Peter Meilstrup
Friday, May 2, 2003
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