Editing Perpetual check (section)

==Mutual perpetual check==
{{Chess diagram  
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|[[John Roycroft|A. J. Roycroft]] (after [[Thomas Rayner Dawson|T. R. Dawson]]), 1976<ref>[https://pdb.dieschwalbe.de/search.jsp?expression=STIP%3D%27perpetual%27%0D%0A ''Die Schwalbe'']</ref>
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|Mutual discovered perpetual check with [[Nightrider (chess)|nightriders]]
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A mutual perpetual check is not possible using only the orthodox chess pieces, but it is possible using some [[fairy chess piece]]s. In the diagram, the pieces represented as inverted knights are [[nightrider (chess)|nightriders]]: they move any number of knight moves in a given direction until they are blocked by any piece along the path (that is, a nightrider is to a knight as a queen is to a king, ignoring the rules on check). There could follow:

:'''1. Ke3+ Kd5+'''
:'''2. Kd3+ Ke5+'''
:'''3. Ke3+ Kd5+'''

and so on. This is in fact a mutual perpetual ''discovered'' check.<ref>Tim Krabbé, [http://timkr.home.xs4all.nl/chess2/diary_6.htm Open chess diary] &ndash; see item 120</ref>
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{{Chess diagram  
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|Noam Elkies, 1999
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|Mutual discovered perpetual check with a camel
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[[Noam Elkies]] devised in 1999 a mutual discovered perpetual check position that requires only one fairy piece. The piece represented by an inverted knight here is a [[camel (chess)|camel]], a (1,3)-leaper. There could follow:
:'''1. Nb5+ Cc5+'''
:'''2. Nd4+ Cb2+'''
:'''3. Nb5+ Cc5+'''
and so on.<ref>Tim Krabbé, [http://timkr.home.xs4all.nl/chess2/diary_7.htm Open chess diary] &ndash; see item 125</ref>

[[Xiangqi]] and [[janggi]], due to the presence of their cannon pieces, can also have mutual perpetual check.
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