#17, #18 You are correct. I am wrong. I lost and I resign.
Actually, in chess960 there are positions conceivable where you really can lose/win a tempo. ;)
This position is possible: lichess.org/editor/4k3/8/8/3PP3/4PPPP/7P/7P/4K3_w_KQkq_-
While this position is not: lichess.org/editor/4k3/8/8/3PPP2/5PPP/7P/7P/4K3_w_KQkq_-
The difference is that in the first example, 15 pawn captures had been made, which i think should be possible because black starts with 15 pieces. In the second example, 16 pawn captures would have had to been made, which is impossible.
While this position is not: lichess.org/editor/4k3/8/8/3PPP2/5PPP/7P/7P/4K3_w_KQkq_-
The difference is that in the first example, 15 pawn captures had been made, which i think should be possible because black starts with 15 pieces. In the second example, 16 pawn captures would have had to been made, which is impossible.
@jposthuma : Any position containing this 3-pawn structure lichess.org/editor/8/8/8/8/8/7P/6PP/8_w_-_- is impossible to reach as well as this one with only one single pawn only lichess.org/editor/8/8/8/8/8/8/8/P7_w_-_-
Generalizing the last case, it is immediately obvious that actually no position with only one piece can ever be reached. Hence there are already 12*64 impossible positions (take any of the twelve different pieces and put it on an arbitrary square - not promoting pawns on the last rank...) These must be the simplest ones - except for the empty board...
Generalizing the last case, it is immediately obvious that actually no position with only one piece can ever be reached. Hence there are already 12*64 impossible positions (take any of the twelve different pieces and put it on an arbitrary square - not promoting pawns on the last rank...) These must be the simplest ones - except for the empty board...
I found a really nice solution to this puzzle. lichess.org/analysis/2r3r1/8/8/8/8/4k3/4b3/R3K2R_b_KQ_-
It is black to move (so the board is reversed). Why is it impossible? Would it be possible with white to move? Perhaps even @Sarg0n you will not guess this ;)
It is black to move (so the board is reversed). Why is it impossible? Would it be possible with white to move? Perhaps even @Sarg0n you will not guess this ;)
Here's another one. Two positions, again with black to move. All that has changed is the position of a bishop, yet one is possible and one is not. Which is which?
lichess.org/analysis/8/8/8/1kr1bn2/8/3K4/6qr/5n1b_b_-_-
lichess.org/analysis/8/8/8/1kr2n2/3b4/3K4/6qr/5n1b_b_-_-
lichess.org/analysis/8/8/8/1kr1bn2/8/3K4/6qr/5n1b_b_-_-
lichess.org/analysis/8/8/8/1kr2n2/3b4/3K4/6qr/5n1b_b_-_-
#26
The first one is the possible one (with the black bishop on e5).
Don't want to spoil with a solution here.
The first one is the possible one (with the black bishop on e5).
Don't want to spoil with a solution here.
#25 Black to move is an easy win. White to move easy draw.
Question: What does this have to do with yes/no impossible?
Question: What does this have to do with yes/no impossible?
@NobodyReally the position cannot be reached legally. See if you can figure out why as there is more to it than meets the eye :) (#25)
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