n9531l1 wrote:
Here's a proof game for the position at #7725 which EvinSung thinks is illegal.
Right on!
Illegal Position Contest!
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EvinSung wrote:
#7766 is clearly illegal. But also simpler than its predecessors!
Arisktotle wrote:
EvinSung wrote:
#7766 is clearly illegal. But also simpler than its predecessors!
Here's what I'm guessing is the easy illegality explanation Arisktotle has in mind.
White's first retraction to uncheck the black king had to be -Bc7xb8. It had to be an uncapture, or else there had to be a black unit at c8 to block queen checks, to give Black a previous move. The capture on b8 or c8, added to the 14 captures by the white pawns, means White needs 15 captures, but Black is only missing 14 units.
EvinSung wrote in #7769:
Is legal!
EvinSung wrote:
#7769
Seems legal to me.
EvinSung wrote in #7771:
Legal.
gxf5 b7#
This is so people can see what #7771 looked like before EvinSung deleted it.
EvinSung wrote:
#7775
The g6 pawn must have originally started on the g-file. Rg7 needs to be set up before the bishops, but both bishops have to be set up before g7-g6 is played, so either Rg7 is impossible or one of the bishops cannot be set up.
Leither123 wrote:
EvinSung wrote in #7775:#7775
The g6 pawn must have originally started on the g-file. Rg7 needs to be set up before the bishops, but both bishops have to be set up before g7-g6 is played, so either Rg7 is impossible or one of the bishops cannot be set up.
This is an example of an illegal island. No matter what else is on the board and where, the structure in the upper right is illegal all by itself. I created several retro-problems with such islands. It's very frustrating to unwind a messy diagram and then discover there was an illegal island on the board all the time which you will never ever release. Watch out for those before you waste your time on constructing a proof game!
Nobody seemed interested in my easy position last time, so here is a slightly harder one.
Is this thing still active and happening?
If so - easy peasy
otherwise, ignore this xD
This thing is still active and happening, but we usually ignore positions with adjacent kings.