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Putnam 2014 B5

Source:

December 8, 2014
Putnamabstract algebragroup theorycollege contestsPutnam 2014Putnam matrices

Problem Statement

In the 75th Annual Putnam Games, participants compete at mathematical games. Patniss and Keeta play a game in which they take turns choosing an element from the group of invertible n×nn\times n matrices with entries in the field Z/pZ\mathbb{Z}/p\mathbb{Z} of integers modulo p,p, where nn is a fixed positive integer and pp is a fixed prime number. The rules of the game are:
(1) A player cannot choose an element that has been chosen by either player on any previous turn.
(2) A player can only choose an element that commutes with all previously chosen elements.
(3) A player who cannot choose an element on his/her turn loses the game.
Patniss takes the first turn. Which player has a winning strategy?