Solution
= Solution
By the <generalized pigeonhole principle>, \b[13 cards] guarantee $\lceil13/4\rceil=4$ cards in one suit. The guarantee is sharp: 12 cards can consist of three cards from each suit, with no four cards of a common suit.
= Solution
By the <generalized pigeonhole principle>, \b[13 cards] guarantee $\lceil13/4\rceil=4$ cards in one suit. The guarantee is sharp: 12 cards can consist of three cards from each suit, with no four cards of a common suit.