Yes Hans -- many thanks! Those two diagrams (Loyd+Lapierre) are true gems. There is a third one, which I will find soon, where there is, for sure, a mate in two -- but impossible to give. Best, É. -----Message d'origine----- De : math-fun [mailto:math-fun-bounces@mailman.xmission.com] De la part de Hans Havermann Envoyé : mardi 2 mai 2017 16:29 À : math-fun <math-fun@mailman.xmission.com> Objet : Re: [math-fun] very tricky mate in 2 EA: "In order to forbid Black to short-castle White has to long-castle." The 'mutually exclusive castling' composition by Armand Lapierre appeared in 1959. Miroslav Havel was apparently the first to notice the possibility of such a thing and used it in 1922: http://b3rn0ull1.blogspot.ca/2012/03/unexpected.html RWG's tricky mate is by Samuel Loyd, 1859. _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com https://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun