[Retros] Backhome proof game.

[Nicolas.Dupont at math.univ-lille1.fr]

Dear retro friends,

In a backhome proof game, every unpromoted officer must go back to its
home square if legally possible (in the orthodox sense). When several
officers can, the choice is free. There is no such obligation for a
promoted unit. A return primes a check.

Example 1 : 1.d4 e5 2.d5 Bb4 3.Kd2 is a sound bpg. Instead of 3.Kd2, 3.d6
is impossible (self-check).

Example 2 : 1.e4 d6 2.Qh5 Bg4 3.f3 Bc8 4.g4 Kd7 5.Qb5 is a sound bpg too.
Black king is under check but not checkmate, as 5...Ke8 would be a
self-check. So black can play 5...Ke6, making his King "free".

This new fairy condition (a kind of variation I found of Bedoni's
nostalgic chess) is accepted in Trillon's Memoriam tournament. I think it
might give some surprising effects. Illustrating puzzle :

rnbq1b1r/pppppkpp/8/4P1P1/8/8/PPPP1P1P/RNBQKBNR
PG 7.5 Backhome

I will give the expected answer (hoping it is unique !) in a couple of days.

Best,

Nicolas.