White to move and NOT checkmate in one

can we talk about why white promoted to a bishop?

No! The why is solely a free choice by the composer of the puzzle. You can never ask why any move before a diagram of any puzzle was played, however bad. You can only ask whether or not a diagram is legal - which implies a legal game must exist that leads to the diagram even when the rating level of that game is "-100,000". If no legal game is possible, then the puzzle is illegal or a joke puzzle or a fairy puzzle. Fairies are played with non-standard but known rules.

Another thing is why the composer (not white) wanted two light-squared white bishops. The answer is simple. If one of the bishops were a queen then it could have played moves without checkmate in the diagram and that is not desirable for the goal of the puzzle!

??

White to move

What's the connection with the puzzles in this topic ??

oh true there's mate in one

I see; there is no mate in 1 for white. It's not hard to make a puzzle like that. For instance white cannot checkmate in 1 in the starting position of any chess game. The fun of the puzzles is that there are so many ways to checkmate in 1 that it is hard to find a move that does not!

if you were referring to my post, it seems we posted at the same time and I was talking about Kyobir's post

I referred to Kyobirs post. He has gone a bit cryptic on me!

It would be mate in 1 if it was black to move.

Either way it’s mate. White to move is checkmate in one, Black to move is already stalemate.

But white cannot move.

oops! sorry. i meant the colors reversed

wow

The expression "White to move ...." only means it's his turn to move after black moved last (which is quite possible). It does not imply that white can actually move. So it is indeed stalemate!

The move only goes to black when you can prove that black could not have played the last move! And even when black is on move, he cannot carry out the instruction in the title which specifically demands it of white.

Meaning the puzzle is invalid?

Of course! Invalid as in unsolvable. Though I assume Kyobir meant his puzzle as a joke

For the one on post 8:

1.exf6 (en passant) Kd6. The only move Black can possibly have made is f7-f5. It was not f6-f5 because White would have been in check with Black to move.

Nope, not a joke - see post 39

It is similar to the following problem I have given before as White to move and mate in 2. Requires retrograde analysis to solve.