not overflow—thus, the game never ends. The player can end the game at any time by waiting for blocks to reach the top, then performing a special action (for example, right-click instead of left-click). Some versions have player lives. If a player reaches a losing condition one time, the game does not end; instead, a life is lost. If all lives are lost, the game ends. In the "continuous" variant, whenever a vertical set of blocks has been cleared and the remaining blocks have shifted to one side, a new, randomly selected column of blocks will pop up on the other side, thereby allowing a game to be played for an extended amount of time. In the "shift" variant, when a set of blocks has been cleared, all remaining blocks to the top and left will shift down and to the right. The "megashift" variant is a combination of the rules of the "continuous" and "shift" variations. Scoring Most versions of the game give points for removing tiles at once, where or , depending on the implementation. For instance, Insane Game for Texas Instruments calculators uses ; Ikuo Hirohata's implementation uses the formula . The Bubble Breaker implementation for Windows Mobile uses the formula. The 2001 version released by Jeff Reno uses the formula . Some versions also offer a large bonus for removing all blocks from the screen, or leaving no more than a certain number of blocks. Others reduce the final score based on the number of blocks remaining at the end of the game. Some game versions award bonus points for clearing the field quickly, encouraging faster play. The faster the player finishes the level, the bigger the bonus. Still others offer combination, or chain, bonuses for clearing the same color of blocks two or more times in succession. Another scoring technique awards bonus points for each chain of a certain color that has a certain number of blocks (for example, two red blocks or 11 blue blocks). After receiving the bonus once, sometimes the bonus condition changes. BPop uses this scoring variation. Some versions have a simple scoring system: each block removed is worth one point, and there is no bonus for removing more than two blocks at a time. This is seen in the Same Pets and Same Hearths variants. Goal-based scoring Some versions award scores based on the attainment of goals. This is typically