There are two piles of matches. Each pile has $$6$$ matches. Cindy and Doris take turns to pick up matches from either pile. There is no limit to how many matches they can pick up, but they must pick up at least one match each turn. The person who picks up the last match will be the winner. If Cindy starts picking up matches first,~\uline{~~~~~~~~~~}~will definitely be the winner (has a winning strategy). 
Overseas Competition->Knowledge Point->Combinatorics->Strategies and Operations->Game Strategy
Doris will be the winner, since she can simply mirror the number of matches Cindy picks up every turn. 