Deck
Source: 17-th Iranian Mathematical Olympiad 1999/2000
December 14, 2005
combinatorics proposedcombinatorics
Problem Statement
In a deck of cards, some digits from toare written on each card.
A digit may occur more than once, but at most once on a certain card.
On each card at least one digit is written, and no two cards are denoted
by the same set of digits. Suppose that for every digits, the
number of cards that contain at least one of them is even. Find .