Playground

Match-one deck maker

Every two cards in this deck share exactly one picture. The cards are the lines of a projective plane of order q, and the pictures are its points: card j holds the pictures for the points of D + j, where D is a Singer difference set. Choose a size, browse the cards, race through the matching game, check the deck, or print it and cut it out. Every picture is upright and the same size, and each one visits each slot on the card exactly once.

The link in your address bar remembers the size, theme, and shuffle, so you can share a deck. Why it works is the subject of Lesson 18.