2 | Giving check is forbidden, unless it is a checkmate.
5 Neither player is allowed to give a check, with the exception of checkmate.
6 Thus, the king is much more powerful than in orthodox chess: as long as
7 he can (potentially) escape, he doesn't fear attacks.
8 So the king can be used to defend pieces in an unusual way.
11 On the following diagram, 1.Qxa6 threatens 2.Bb6
12 with a mate to follow by Qxa7.
13 The black rook cannot take because it would check the white king.
15 figure.diagram-container
17 | fen:1k1r1b2/rP1b2p1/pQ1pp1nq/K4p1p/P4PnP/2PN2P1/3PP1B1/R1RN2B1:
18 figcaption 1.Qxd8+ is forbidden because 1...Bc8 would be possible.
23 1.Qf7# is checkmate on the left diagram, because if the king takes
24 then the rook on h8 gives check but not checkmate.
25 However, on the right diagram 1.Qf7+ runs into 1...Kxf7#, which is now
26 a legal move because the white king is checkmated.
28 figure.diagram-container
30 | fen:K5kr/8/5Q2/8/8/8/8/8:
32 | fen:K5kr/RB6/5Q2/8/8/8/8/7b:
33 figcaption 1.Qf7 mates on the left, but not on the right.
38 a(href="https://www.chessvariants.com/usualeq.dir/checklss.html")
40 | on chessvariants.com, and the
41 a(href="https://en.wikipedia.org/wiki/Checkless_chess") Wikipedia page