Calculation Training

@ Spaceysmile 

Read the precedent message we have already speak about that 4.Bb4 5.Rc1 threatening Rb1 or Ra1+ then Rb1 in some case and we stoped here. I think there is no defense because 5.Ba5 6.Ra1; Kb6 7.Rb1 wins and also 5.Bg8 6.Rg1; Be6 7.Rg7+; Kb8 8.Rb7+ so yeah I see no defense.

puzzle 13 is really impressive after seeing the input from everyone suggesting Kh1 at the right moment. i did my best to calculate without moving pieces and spent....a long time hehe...coming up with variations. not once did i consider the possibility of a positional zugzwang. Incredible puzzle!

it's a trick when you solve a difficult study always wonder what happens if you do nothing.

It is a good point, and it wasn't until I reached the end of all my calculations that I tried to find something like this, but they all seemed to allow black to save his material. I guess my original comment about "not once did i consider" wasn't completely true, but i didn't give it much credence after failing to find such a concept at the end of my calculations. it would have to be something to consider at many points i see.

What makes it a little more impressive is that it is necessary to threaten the bishop with the rook on c6 instead of c3. considering that regardless of which of the two squares the rook is on between c3 and c6, black's lightsquare bishop will only be able to maintain the two safe squares of b3 or e6. it doesn't work because the king would have a way out of the corner with the rook on c3 and it would no longer provide the same threat.

...or rather, it would allow black a tempo to get the darksquare bishop to a better square as to remove some of white's threats.

This is a good tip to have in the back of your mind when doing puzzles; zugswang - what happens if you do nothing. 

Yes, the Kh1 idea in this puzzle impressed me too.

Here is the 13th Official Puzzle Solution

Everyone did really well solving this one, but I think IM @pfren was the first to find the Kh1 zugswang idea. I think for the next puzzles I'll keep them coming, but I'll give more time between when the solution is found and when I post a new puzzle - so more members can attempt them.

I'll post the 14th puzzle soon though

14th Official Puzzle. White to move and win. 

Another puzzle given to me by kJDG12. 

This one is really easy actually. I solved it in around 20 seconds. 
1. Nd6!! b1=Q (1...Kxd6 2. Rd4+ with Rs1 next preventing promotion) 2. Rd4!! Kxd4 3. Nb5+ If 3... Kd5 or Ke4, 4. Nc3+ forks the king and queen. If 3...Kc4, 4. Na3+ forks the king and queen. White wins. More of a tactic than a calculation exercise.

Oh shoot. I just realized that I missed that Black doesn’t have to take the rook on d4 and can play Ke6 or Kc6. Oops. I’m pretty sure I’m on the right track, though.

Do more puzzles!

So, then the answer is to force black to take the rook .  Change the move order:

Rd4+ Kxd4 Nd6...etc.

You will have another problem though...in any knight fork/pawn promotion puzzle like this you have to also figure out what happens if the pawn is promoted to a knight, preventing your fork at the end.

In this case, the passed f pawn should probably do the job.

The only other real possibility here besides the rook and knight mechanic was to close a mating net with the king (which immediately fails due to check on promotion and so is eliminated).

I think @Chess4PK is on to something so I altered his move order a bit.

1. Rd4+ Kxc4 (forced otherwise the rook makes it to the 1st rank in time)

2. Nd6 b1=Q

3. Nb4+ and now Ke4 or Kc4 is forced. I think Kc4 is slightly better considering it threatens a pawn in front of his last remaining pawn.

If 3. ...Ke4 then 4. Nc3+ forking the king and queen. If 3. ...Kc4 then 4. Na3+ forking king and queen.

In the case of the king and pawn endgame with Kc4 then white can sac his knight for blacks last pawn and push his f-pawn to queen. In the case of the endgame with Ke4 then white can use his knight, king, and pawn to win black's last pawn and queen easily.

All this means that the only move in question in this line would be the response to 2. Nd6. Black only has 4 legal moves in that moment: Kc3, Kd5, b5-b4, or b1=Q. If Kc3 then 3. Ne4+ and anywhere the king goes, white can put the knight on d2 protecting the queening square, and white can support his f-pawn to queening at least 1 move faster than black's b5 pawn in the case black tries to use his king to stop it making it impossible for black to queen on the b-file. If he tries Kd5 then Nb4 threatening a fork if he queens, so he has to move his king, and if he chooses the best king move to threaten the knight, then Na3 is in time to stop the queening pawn with a won endgame. If the king continues to threaten the knight, he can eventually land on d2 which is protected by whites king, if he takes a tempo to take the c-pawn, black won't be able to threaten black's knight when it moves to b1 AND stop white's f-pawn queening. If he tries the last remaining legal move b5-b4, then 3. Nxd4+ anyway with the same continuation as the main line, the only difference being he no longer has the additional threat of queening his last pawn when white is forced to sacrifice the knight for black's first queen.

I hadn't considered an underpromotion preventing some forks, but I also agree about the f-pawn. It should be enough at the very least for a draw, but with the right technique, white should be able to sac his knight to draw the black knight away in some lines.

Whites have to win this position. Draw is not enough.

I think white still wins after 1.Rd4+ Kxd4 2.Nd6 b1N (credit goes to other players who discovered that idea until there ) 3.Nb5+ (that prevents b1-knight moving). Black now have 2 options: go after knight and hope to catch f-pawn , and go after f-pawn and hope to destroy b4 pawn.

1st way: 3..Kc4 4.f5 Kxb5 5.f6 Nc3+ 6.Ke1! and white queens,  and endgame is winning (KQvKNp with pawn not being advanced too much).

2nd way: 3...Ke4 4.Kd1 Kxf4 5.Kc2 Ke4 6.Kxb1 Kd5 7.Na7 Kc4 8.b5 and white protects the pawn. 

I like the discussions and how everyone builds off of ideas previously posted  Solving pretty good for the most part.

I think Spaceysmile found the winning line on 2.b1N There is another possibilty which is 2.Kc3 for blacks threatening either Kc2 or Kb3-a2 and then b1Q. But in this case just 3.Ne4+; Kxb4 4.Nd2 keeping b1 square and the endgame is winning if there is no way for blacks to stalemate.

So far the "correct" idea is 1. Rd4+ Kxd4 2. Nd6 Kc3 (for clarity for everyone else to continue), but then how does White continue after ...Kc3 here? @Spaceysmile did a good job with the b1=N sidelines and showing how White does better.

Yep, this forum is fairly insightful. I’m going to give it a massive I for insight, massive to differentiate it from an electric current. Wait... ZAP