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Problem 4

Part of 2019 CIIM

Problems(1)

CIIM 2019 Problem 4

Source:

8/30/2021
Let (G,)(G, *) a group of n>1n > 1 elements, and let gGg \in G be an element distinct from the identity. Ana and Bob play with the group GG on the following way: Starting with Ana and playing alternately, each player selects an element of GG that has not been selected before, until each element of GG have been selected or a player have selected the elements aa and aga * g for some aGa \in G. In that case it is said that the player loses and his opponent wins.
a)a) If nn is odd, show that, independent of element gg, one of the two players has a winning strategy and determines which player possesses such a strategy.
b)b) If nn is even, show that there exists an element gGg \in G for which none of the players has a winning strategy.
Note: A group (G,)(G, *) es a set GG together with a binary operation :G×GG* : G\times G \to G that satisfy the following properties (i)(i) * is asociative: a,b,cG(ab)c=a(bc)\forall a, b, c \in G (a * b) * c = a * (b * c); (ii)(ii) there exists an identity element eGe \in G such that aG,ae=ea=a;\forall a \in G, a *e = e * a = a; (iii)(iii) there exists inverse elements: aGa1G\forall a \in G \exists a^{-1} \in G such that aa1=a1a=e.a*a^{-1} = a^{-1} *a = e.
CIIM