Editing Perpetual check (section)

==Perpetual pursuit==
{{Chess diagram
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|S. Birnov, 1928
|  |  |  |  |  |  |bd|  
|  |  |kl|  |  |  |  |   
|  |  |  |  |  |  |  |  
|pl|  |pd|  |  |kd|  |  
|  |  |pl|  |  |  |  |pd
|  |  |pl|  |pl|  |  |  
|  |  |  |  |  |  |  |  
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|White to play and draw
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Related to perpetual check is the ''perpetual pursuit'', which differs in that the continually attacked piece is not the king. The result is similar, in that the opposing side's attack stalls because of the need to respond to the continuous threats.<ref>{{cite book |last1=Seirawan |first1=Yasser |author1-link=Yasser Seirawan |last2=Silman |first2=Jeremy |author2-link=Jeremy Silman |date=2003 |title=Winning Chess Tactics |location=London |publisher=Everyman Chess |pages=119–121 |isbn=1857443330}}</ref>

In the Birnov study illustrated, White's situation seems hopeless: they are down a piece and cannot stop Black's h-pawn, and their passed a-pawn can easily be stopped by Black's bishop. However, they can save themself by restricting the bishop's movement to set up a perpetual pursuit. They begin:
:'''1. a6 Bxc4'''
A direct pawn race with 1...h3? fails, as White promotes first and covers the promotion square.
:'''2. e4+!'''
This pawn sacrifice forces Black to limit their bishop's scope along the long diagonal.
:'''2... Kxe4'''
Forced, as Black has to play ...Bd5 to stop the pawn.
:'''3. a7 Bd5'''
:'''4. c4!'''
Denying another square to the bishop, which must stay on the a8–h1 diagonal. This forces
:'''4... Ba8'''
And White can then begin the perpetual pursuit:
:'''5. Kb8 Bc6'''
:'''6. Kc7 Ba8'''
Black can make no progress.

{| align="right" 
|-valign="top" 
|+Bilek vs. Schüssler, 1978
|
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{{Chess diagram small
|tright
|
|rd|nd|  |qd|kd|bd|  |rd
|pd|  |  |  |nd|pd|pd|pd
|  |pd|pd|  |  |  |  |  
|  |  |  |nl|  |  |  |  
|  |  |bl|  |  |  |  |  
|  |  |  |  |  |pl|pl|  
|pl|pl|  |  |  |pl|  |pl
|rl|  |bl|ql|kl|  |  |rl
|White attempts to win the enemy queen...
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{{Chess diagram small
|tright
|
|rd|nd|  |ql|  |bd|  |rd
|pd|  |  |  |  |kd|  |pd
|  |pd|pd|  |  |pd|  |  
|  |  |  |nd|  |  |  |  
|  |  |  |  |  |  |  |  
|  |  |  |  |  |pl|pl|  
|pl|pl|  |  |  |pl|  |pl
|rl|  |bl|  |kl|  |  |rl
|...but traps his own into a perpetual pursuit.
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An example of perpetual pursuit being used in a game occurred in [[István Bilek]]–[[Harry Schüssler]], Poutiainen Memorial 1978. Bilek thought he could win the enemy queen with the combination
:'''10. Nf6+ gxf6'''
:'''11. Bxf7+ Kxf7'''
:'''12. Qxd8'''
However, Schüssler replied
:'''12... Nd5! ½–½'''
and Bilek conceded the draw. His queen is now trapped, and with ...Bb4+ threatening to win it, he has nothing better than 13.0-0 Bg7 14.Qd6 Bf8 15.Qd8 Bg7 with another perpetual pursuit.
{{clear}}