White 20

[cheesehead]

Color me "surprised". Instead of opening the b-file right away, they moved [URL="http://www.mersenneforum.org/showpost.php?p=366097&postcount=125"][B]19 ... Ba6[/B][/URL].

Our deadline is 11 Feb 9:21 GMT.

[I][U]We've already analyzed this position, while considering our 18th move![/U][/I]
[QUOTE=cheesehead;364663][B]18 a4[/B]
< snip >

18 ... b4
19 Nd2 Ba6 20 Rf2 and 21 Bf1 wins the c-pawn.[/QUOTE]
Do we really win the c-pawn?

Time for closer scrutiny, while not neglecting worthy alternatives.

Our candidates are:

[B]20 Rf2[/B]

[B]20 Ne4[/B]

- - -

(plus 32 other legal moves that might or might not have hitherto-unnoticed virtue:

Feel free to skip this part!

This may seem ridiculous, but once in a while it can be a useful exercise to examine every legal move at ones disposal - to clear the cobwebs. So, humor me a while ... if you're actually reading this instead of skipping it.

20 b3 allows 20 ... cxb3 attacking our rook. If 21 Rf2 would be good then, why not 20 Rf2 instead?
20 cxb4 allows 20 ... c3 attacking both rook and knight. No good.
20 d5 -- 20 ... exd5 would make us wonder why we bothered protecting the e5-pawn with d4 earlier. It would give our B/e3 some Q-side scope but ... No.
20 g4 -- deterring ... Nf5 isn't important as long as that would leave the N/c6 [I]en prise[/I] with check.
20 h3 or 20 h4 -- if either has any value, surely it could wait until later to be played.
20 Ra2 or 20 Rb1 or 20 Rc1 --- if has value, surely could wait until later.
20 Ra3 -- Just say no.
20 Nf2 -- Isn't this best left at d1 to protect b2/c3/e3 for right now?
20 Nb1 or 20 Nb3 or Nxc4 -- Just say no.
20 Nf3 -- no redeeming value.
20 any move of the B/e3 -- no redeeming value.
20 Bxc6+ -- needs to be kept in mind for later.
20 Bd5 -- No.
20 Be4 or Bf3 -- just gets in the way of the N/d2 or R/f1
20 Bh3 -- needs to be kept in mind for possible later use.
20 Bh1 -- no redeeming value.
20 Re1 -- leave this rook on the f-file, please.
20 Rf3-4-5-6 or xf7 -- not now.
20 K moves -- can only get in the way
Okay, I got that out of my system.)

[LaurV]

I think our last discussion about this path was ([URL="http://www.mersenneforum.org/www.mersenneforum.org/showthread.php?p=365520"]see here[/URL]):

[QUOTE][B]19 ... Ba6 20 Ne4 O-O[/B]
[B]21.Nf6!
[/B][/QUOTE]This may be our win... Any other reply beside of the castling seemed to be worse for them. And with castling, we get the h6 pawn, as discussed. We only need to analyze if they can't do bad things on the queen's flank (b4xc3, etc??? any chance?), or we didn't miss something obvious.

Yeaaahh... the optimistic sentiment is coming again. We won this game! :w00t:

[WMHalsdorf]

Not surprised by Ba6, they probably plan on bxc as their next move not realizing that out intent is not the queen's side but exploiting f6 with Ne4.

[cheesehead]

[QUOTE=LaurV;366114]I think our last discussion about this path was ([URL="http://www.mersenneforum.org/www.mersenneforum.org/showthread.php?p=365520"]see here[/URL]):[/quote](Correct link is [url]http://www.mersenneforum.org/showthread.php?p=365520[/url])

Right. Thanks. :-)

[QUOTE=WMHalsdorf;366132]Not surprised by Ba6, they probably plan on bxc as their next move not realizing that out intent is not the queen's side but exploiting f6 with Ne4.[/QUOTE]Let's always be careful about underestimating our opponent.

[QUOTE=LaurV;366114]This may be our win... Any other reply beside of the castling seemed to be worse for them. And with castling, we get the h6 pawn, as discussed. We only need to analyze if they can't do bad things on the queen's flank (b4xc3, etc??? any chance?)[/QUOTE]Exactly.

[b]20 Ne4[/b]

[b]20 ... bxc3 21 bxc3[/b]

Now, suppose [b]21 ... Rb3[/b].

[b]22 Nf6+[/b] Bxf6 23 exf6 Nd5 doesn't get us the h-pawn in this position.

[b]22 Nd6+[/b]
If 22 ... Kd8 23 Nxf7+ winning the Exchange and pawn.
If 22 ... Kd7 23 Rxf7 (threatening 24 Bxc6+ Kxc6 25 Rxe7) ... Bf8 (or 23 ... Rb6 24 Rxg7) 24 Bxh6 Rxh6 25 Rxf8 and we're a pawn up but need to activate our QR and N/d1.
If 22 ... Kf8 23 Rxf7+ Kg8 24 Bh3 Bc8 25 Rxg7+ Kxg7 26 Nxc8 Nxc8 27 Bxe6 Nb6 28 Bd2 Re8 (else 29 Ne3) 29 Bg4 we'd have a piece and two passed pawns (plus designs on another) for a rook.

(Suppose Black makes a different move 21.
[b]21 ... ??? [/b])

What if we check on d6 before retaking on c3?
[b]20 ... bxc3 21 Nd6+[/b]
Black's responses are the same as above, [i]but[/i] if we don't check or take on c3 on move 22, Black has 22 ... cxb2 or 22 ... c2

(To be continued ... I have to stop now)

[cheesehead]

[QUOTE=cheesehead;366110]

Our deadline is 11 Feb 9:21 GMT.

[/QUOTE]BTW, that's _Tuesday_, 11 Feb 9:21 GMT.

[cheesehead]

It seems to me that [B]20 Ne4[/B] is our best move, and we might as well post it now.

- - -

[QUOTE=cheesehead;366180][B]20 Ne4[/B]

[B]20 ... bxc3 21 bxc3[/B]

Now, suppose [B]21 ... Rb3[/B].

< snip >
[B]22 Nd6+[/B]
< snip >
If 22 ... Kd7 23 Rxf7 (threatening 24 Bxc6+ Kxc6 25 Rxe7) ... Bf8 (or 23 ... Rb6 24 Rxg7) 24 Bxh6 Rxh6 25 Rxf8 and we're[/QUOTE]two pawns[quote]up but need to activate our QR and N/d1.[/quote]- - -

[QUOTE=cheesehead;366180][B]20 Ne4[/B]

[B]20 ... bxc3 21 bxc3[/B]

Now, suppose [B]21 ... Rb3[/B].

< snip >

[B]22 Nd6+[/B]
< snip >
If 22 ... Kf8 23 Rxf7+[/QUOTE]Stronger would be 23 Nxf7.
If 23 ... Rh7 24 Ng5+ Kg8 25 Nxh7 Kxh7 26 Bh3
If 23 ... Rg8 24 Nxh6+

- - -

[QUOTE=cheesehead;366180][B]20 Ne4[/B]
< snip >

What if we check on d6 before retaking on c3?
[B]20 ... bxc3 21 Nd6+[/B]
Black's responses are the same as above, [I]but[/I] if we don't check or take on c3 on move 22, Black has 22 ... cxb2 or 22 ... c2 [/QUOTE]After looking further, I see no advantage to 21 Nd6+ here. The tempo we save by not retaking on c3 immediately simply has to be used later to re-take on c3, lest we be worse off.

- - -

There remains the question:
[QUOTE=cheesehead;366180][B]20 Ne4[/B]

[B]20 ... bxc3 21 bxc3[/B]

< snip >

(Suppose Black makes a different move 21.
[B]21 ... ??? [/B])[/QUOTE]

[cheesehead]

[QUOTE=cheesehead;366180][B]20 Ne4[/B]

[B]20 ... bxc3 21 bxc3[/B]

Now, suppose [B]21 ... Rb3[/B].
[/QUOTE]... and that's the only reasonable move for that rook on that move.
21 ... Rb7 just loses the Exchange after 22 Nd6+.
21 ... Rb6 would protect the N/c6 so that after ... O-O, Nf6+, ... Bxf6 and exf6, ... Nf5 doesn't lose a piece -- but then we'd play Nd6+ before Black castles, so that line wouldn't ever happen.
Any other R/b8 move subjects it to immediate capture or takes it off the just-opened b-file.

- - -

What's else to consider?

[QUOTE=cheesehead;366110]
[B]20 Rf2[/B][/QUOTE]This would make sense if we're actually trying to win the pawn/c4 with [B]21 Bf1[/B]. Black could defend that pawn with 20 ... Rc8 and 21 ... N/c6 moves (to a7,b8 or d8), but then that knight seems at least as much out of the action as our N/d1.

But lets look further:
[B]20 ... Rc8 21 Bf1[/B]
If 21 ... Nd8 22 Ne4 O-O 23 Nc5 Bb7 24 Bxc4 and we've won the c-pawn.
If 21 ... Na7 22 Ne4 O-O 23 Nc5 Rc6 24 Nxa6 Rxa6 25 Bxc4 and again we've won the c-pawn.

But [B]21 ... Nb8 22 Ne4 O-O 23 Nc5 Nd5 24 Nxa6 Nxa6 25 Nb2 Nb6[/B] and the c-pawn is still defended because Black has just enough time to configure his knights to do so. (A black knight on the back rank can defend almost as well as a white knight on the back rank. :-))

So, I don't see enough merit for [B]20 Rf2[/B].

- - -

I think the last loose end is that pesky question about what else Black might do on move 21 (besides what we've already considered) after [B]20 Ne4[/B][B] bxc3 21 bxc3[/B]. I don't yet see anything else that could be useful for Black there.

[LaurV]

I went through all your analysis from the last post. I fully agree that Ne4 is much better that Rf2. But now, if you talk about Rb3, we could avoid it if we play [B]20.Nf2[/B]. This is at least as good as Rf2, if not better. Lets see: Now, after ...bxc3, 21.bxc3 they cant play the rook to b3, so most probably 21...Nd5 (not many choices here...) and then 22. Nf2e4, we stay very good now. The problem is they could play 20...Nd5 first. Then what? 21.Nf2e4, they can't take the bishop, because Nd6 and rook take f7, black is dead. But still, after 21...castling, we may Nf6 (already discussed, but it was the other horse, what is different now?? do we need to defend the bishop and need to lose moves retreating it, or we can ignore it and continue the attach?)

BRB, this version is very interesting...

[edit, well, they can defend the f7 pawn with 21..Nd8, we most probably have to move/defend the bishop, and d2 is busy by the horse, so only Ra1e1 makes sense, as retreating Bf2 is bad, it blocks the rook, etc. So, this version is worse than 20.Rf2]

We should play 20.Ne4 now. I mean, not right now, but just saying that Ne4 is the best move we can do in this position.

[cheesehead]

[QUOTE=LaurV;366294]< snip > [B]20.Nf2[/B]. < snip >
[B]20...Nd5[/B] < snip > [B]21.Nf2e4[/B], they can't take the bishop,[/QUOTE]Actually, they can. 21 ... Nxe3 22 Nd6+ Kd8 23 Rxf7 Nxg2 24 Rxg7 Ne3 and Black has captured both of our bishops in exchange for a bishop and pawn ...

... but we can pick off several more pawns. E.g., 25 Rxg6 Kd7 (preventing Rxe6) 26 Rg7+ Kd8 27 Re1 Nf5 28 Nxf5 exf5 29 Rg6 Bb7 (not ... Ne7 30 Rxa6 or ... Rf8 30 Rxc6) 30 Rf6 Ne7 31 Nxc4 (we finally get the third pawn in exchange for our bishop) Ra8 32 Nd6 Bc6 33 Nxf5 Bxa4 34 Nxh6 (getting our fourth pawn for the bishop) Bb3 (preventing 35 Nf7+ from winning a rook) 35 R1f1 (threat Rf8+) Re8 36 Rf8 Kd7 and we have four pawns for the bishop but it's still a struggle.

[quote]But still, after 21...castling, we may Nf6 (already discussed, but it was the other horse, what is different now??[/quote]Now, we don't have a defender for the e3 bishop (or c3 pawn). We do have connected rooks, however.

[quote]do we need to defend the bishop and need to lose moves retreating it, or we can ignore it and continue the attach?)[/quote][B]21 ... O-O 22 Nf6+ Bxf6[/B] (not ... Nxf6 23 exf6 Bh8 24 Bxh6) [B]23 exf6 Nxe3[/B].
If 24 Bxc6 Nxf1 25 Rxf1 bxc3 26 bxc3 Rb2 27 Ne4 R8b8, then Black can force a rook exchange, and then we lose.
If 24 Rf2 Nxg2 25 Kxg2 bxc3 26 bxc3 and ... whoops, we're down a whole bishop.

So I think we can't afford to allow ... Nxe3 without immediate re-take.

- - -

But we may have something better. Note what I said above about Black's having just enough time (none to spare) to meet our Rf2 and Bf1 threat. Can we interleave our two different threats, leaving Black unable to meet both?

I haven't figured it all out yet, but it starts with
[b]20 Rf2 Rc8[/b] (forced, else Black can't meet 21 Bf1)
[b]21 Bf1 Nb8[/b] (again, forced)
( But remember that ... bxc3, bxc3 can be interpolated any time here )
[b]22 Ne4 O-O 23 Nd6[/b] (this is where I deviate from previous analysis in post #7)
Now 23 ... Nd5 isn't feasible.
If 23 ... Rc6 or Rc7 24 Bd2 (threatening to attack c4 a third time with 25 Ne3. Here ... Nd5 has no threat to capture our bishop. Black can't add a third defender with Rfc8 yet.) Nc8 25 Nb5 Bxb5 26 axb5.
Now Black's only defense of a5 is 26 ... Ra7, but that allows us to capture the c4 pawn with 27 Bxc4. 27 ... Nb6 chases the bishop back, but too late to save the c-pawn.

[cheesehead]

In the [B]20 Rf2[/B] line, Black has a resource I overlooked. It doesn't necessarily refute it or make 20 Ne4 automatically better, but needs analysis.

[QUOTE=cheesehead;366314]
[B]20 Rf2 Rc8[/B] (forced, else Black can't meet 21 Bf1)[/QUOTE][I]No, not forced after all:[/I]
[B]20 ... O-O 21 Bf1 Rfc8[/B]

If 22 Nxc4 Bxc4 23 Bxc4 Nxe5!
If now 24 Ba6 Rc6 25 Be2 Nc4 26 Bf3 Nxe3 27 Bxc6 Nxd1 28 Rxd1 Nxc6 and Black would have two pieces for his rook.
Better: 24 Bxe6 fxe6 25 dxe5 Bxe5 26 Bxh6 bxc3 27 bxc3 Bxc3 28 Nxc3 Rxc3 (or 28 R1a2 Bd4 29 Be3) and material is even. We haven't won a pawn, but Black's remaining king-side pawns are not connected, so we have that slim edge.

If 22 Bxc4 Bxc4 23 Nxc4 and we're a pawn up momentarily, but 23 ... Nd5 24 Bd2 cxb3 25 cxb3 Nxe5! 26 Nd6 Rd8 27 dxe5 Bxe5 28 Nb5 leaves us down a pawn and probably losing another.
(If 23 ... Nxd4 24 Nd6 and Black loses either the Exchange or a knight.)

Still murky. We have a few more days for analysis of whether [B]20 Rf2[/B] can force as much advantage for us as [B]20 Ne4[/B].

[B]20 Ne4[/B] remains our best move until proven otherwise.

- - -

I may not have much time for analysis in the next few days. If you don't hear from me, just post [b]20 Ne4[/b].

[cheesehead]

After [B]20 Nd4 O-O 21 Nf6+ Bxf6[/B] there is an alternative to 22 exf6:
[B]22 Rxf6[/B].

Here, 22 ... Nd5 would lose a piece after 23 Bxd5 exd5 24 Rxc6.

But what if 22 ... Nf5, trapping our rook? First, it leaves a knight [I]en prise[/I]: 23 Bxc6. Our rook is temporarily safe because Black's dark-square bishop is gone. Furthermore, we have possibilities to persuade the f5 knight to move (g4) or to capture it (Be4-f5) such that re-capture with a pawn will free our rook one way or another. In the worst case, Rxf5 leaves us with two pieces for the rook, and Black with doubled f-pawns. Alternatively, Bxh6 would force Black to release our rook if he wants to take the B/h6 with the N/f5.