Half the variations which are calculated in a tournament game turn out to be completely superfluous. Unfortunately, no one knows in advance which half.
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[Event "rated untimed match"]
[Site "?"]
[Date "????.??.??"]
[Round "?"]
[White "White player"]
[Black "Black player"]
[Result "*"]
[BlackElo "0"]
[FEN "R7/6k1/6p1/8/P4P2/6K1/r4P2/8 w - - 0 1"]
[SetUp "1"]
[TimeControl "0"]
[WhiteElo "0"]
{ White Wins with Forcing Moves } 1. a5 { White aims to force the black king to
remain on the g7 and h7 squares. } ( { Hasty moves like this end up in a draw. } 1. f5 gxf5 2. a5 Kf6 3. a6 Ra3+ 4. Kf4 Ra4+ 5. Ke3 Kg5 6. a7 Ra3+ 7. Kd4 Kf4 { Black uses his pawn to shield himself from an otherwise game-winning check.
Draw. } ) 1... Kf6 2. a6 Kf7 ( { Black dare not try: } 2... g5 3. fxg5+ Kxg5 { Now
the black king cannot return to g7 or h7 in time. } 4. a7 Ra3+ 5. f3 Kf6 6. Rf8+ Ke7 7. a8=Q Rxa8 8. Rxa8 { White wins with a large material advantage. } ) 3. a7 Kg7 { The black king is now confined to g7 and h7. } 4. f5 { Kf3 also
wins, but his move clarifies the pawn situation. } 4... gxf5 5. f4 { The white king
will wander around to the queen side of the board at his leisure. Then it
will capture the pawn which cannot be guarded for long due to Zugzwang. } 5... Kh7 6. Kf3 Ra3+ { Black's checks only delay the inevitable. } 7. Ke2 Kg7 8. Kd2 Kh7 9. Kc2 Kg7 10. Kb2 Ra4 11. Kb3 Ra6 12. Kb4 Ra1 13. Kc5 Ra3 14. Kd5 Ra2 15. Ke5 Ra5+ 16. Ke6 Kh7 17. Kf6 { Black must move. } 17... Ra1 18. Kxf5 Kg7 19. Ke5 Re1+ { Black's checks only delay the inevitable. } 20. Kd4 Rd1+ 21. Ke3 Re1+ 22. Kd2 Ra1 23. f5 Ra3 24. f6+ Kf7 ( { Black can try: } 24... Kh7 25. f7 Ra2+ 26. Kc3 Ra3+ 27. Kb2 Ra6 28. f8=Q { White wins with a large material advantage. } ) 25. Rh8 Rxa7 26. Rh7+ Kxf6 27. Rxa7 { White wins with a large material advantage. } *