Contribute correction: Challenger Reversi

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|  __ \\    / _ \\    ____     /_   _// 
| |  \ ||  / //\ \\  |    \\    -| ||-  
| |__/ || |  ___  || | [] ||    _| ||_  
|_____//  |_||  |_|| |  __//   /_____// 
 -----`   `-`   `-`  |_|`-`    `-----`  
                     `-`