There are two piles of matches, six in one pile and six in the other pile. Andy and Bob take turns to take the matches from any one of the two piles. The number of matches they can take is unlimited, but they have to take at least one each turn. Whoever picks the last match is the winner. If Andy takes the first match,  is guarantee to win. 
Overseas Competition->Knowledge Point->Combinatorics->Strategies and Operations->Game Strategy
The number of matches in the two piles is the same. No matter how many matches Andy takes from one pile, Bob just needs to take the same amount of matches from the other pile. As long as there are matches for Andy to take, Bob can definitely take away the same amount from the other pile. Therefore, Bob will take away the last match and he is guarantee to win. 