The object of the game is to identify the 6 'Sets',
of three cards each, from 12 cards laid out on the screen. Each card has
a variation of the following four features:
1.COLOR: Each card is red, green, or purple.
2.SYMBOL: Each card contains ovals, squiggles, or diamonds.
3.NUMBER: Each card has one, two, or three symbols.
4.SHADING: Each card is solid, open, or striped.
A 'Set' consists of three cards in which each feature
is EITHER the same on each card OR is different on each card. That is
to say, any feature in the 'Set' of three cards is either
common to all three cards or is different on each card.