Dann Corbit wrote:Obvious cases like this:
[d] 3k4/3q1P1q/8/8/8/8/3QP3/4K3 w - -
Not a very convincing example, as 1. f8=N would leave you after 1... Qh1+ 2. Kf2 Qxd2 with one Knight against two Queens, while 1. f8=Q+ would have you left 2Q vs 2Q. But I understand that you are thinking of a fork attack on two Queens. But the presence of two Queens would of course be a rarity in itself. But even when forking two Queens you should expect the Queens to protect each other, so that you would in the end just give your Pawn to make an opponent Queen go away. Which is equivalent to getting a Queen yourself.
You are right, however, in that one can always devise tactical situations where promoting to Knight is the best move. But if it is not a check, giving it the same status as a bad capture is probably deserved.
Excuse me, but the following line is better for the side to move (white): Qxd7+, Kxd7; f8=N+ and the endgame is a winning KNPk.
Checking with SF 6, it is a checkmate in four: f8=Q+, Kc7; Qa5+, Kc6; Qfc5+, Kb7; Qaa7#.
Ah, OK. But in that case the promotion to Knight was a check, so it isn't really an example of a case where you would want to consider an non-checking under-promotion.
Dann Corbit wrote:Obvious cases like this:
[d] 3k4/3q1P1q/8/8/8/8/3QP3/4K3 w - -
Not a very convincing example, as 1. f8=N would leave you after 1... Qh1+ 2. Kf2 Qxd2 with one Knight against two Queens, while 1. f8=Q+ would have you left 2Q vs 2Q. But I understand that you are thinking of a fork attack on two Queens. But the presence of two Queens would of course be a rarity in itself. But even when forking two Queens you should expect the Queens to protect each other, so that you would in the end just give your Pawn to make an opponent Queen go away. Which is equivalent to getting a Queen yourself.
You are right, however, in that one can always devise tactical situations where promoting to Knight is the best move. But if it is not a check, giving it the same status as a bad capture is probably deserved.
What if rays are best in a promoted pawn, but the extra rays of a Queen would induce stalemate, so a bishop or rook is preferred? An extremely rare circumstance of course.
This is from a Stockfish-vs-Stockfish very fast game:
[d]8/P1kP4/4P3/2P5/3K2N1/8/8/8 w - -
The game continued with a8=R, because getting a queen would have been stalemate.
It was an interesting bug: I've added a bit to say "this is a losing move" that I use only at the root (losing move means the one that get mated). Do to my mistake, the bit was the same as the type of promotion for knight... so anytime that the best move were an under-promotion to knight the engine think as it was a losing move!!! It was almost impossible to find it in a true game...
