Vianiato PopOut

Vianiato PopOut is a Connect-4 variant called PopOut. The search engine uses alpha-beta pruning together with several enhancements to prove that the game is a first-player win. In fact, the first player can always win within 21 moves (plies) if the player starts in the middle column.

Pop Out starts the same as traditional gameplay, with an empty board and players alternating turns placing their own colored discs into the board. During each turn, a player can either add another disc from the top or, if one has any discs of his or her own color on the bottom row, remove (or "pop out") a disc of one's own color from the bottom.

Popping a disc out from the bottom drops every disc above it down one space, changing their relationship with the rest of the board and changing the possibilities for a connection. The first player to connect four of their discs horizontally, vertically, or diagonally wins the game.