Four Blunders

Chess Informant 91/412 is the game Xu Jun -- Pendyala Harikrishna, Tripoli 2004. In the annotations, Xu Jun identifies his move 23 as a blunder. This error is followed by Harikrishna's move 23 blunder, another White blunder on move 24 and another Black blunder in reply. Jun went on to win. Here, Harikrishna missed his first chance to score the point.

Black to move

Everyone errs. Errors produce training positions.