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Old 2014-03-20, 13:33   #1
WMHalsdorf
 
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Default White 24

I didn't see any analysis for 24. Bf4 Rxf4 which opens up the center in what appears to favor Black more than us despite the material advantage we gain.
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Old 2014-03-20, 16:20   #2
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They re-took with the rook: 23 ... Rxf6

Our deadline is [URL="http://mersenneforum.org/showpost.php?p=369483&postcount=134"]Thursday, March 27 12:40 GMT[/URL]

--------------------------------------------------------------------------
[QUOTE=WMHalsdorf;369486]I didn't see any analysis for 24. Bf4 Rxf4[/QUOTE]Thank you for that reminder! I see that I'd not yet posted that, or yet looked at it more than a move.

[quote]which opens up the center in what appears to favor Black more than us[/quote]Yes, it does.

If 25 gxf4 Nxd4 then (speculation) if 26 Ne3 bxc3 27 bxc3 Ne2+ and now:
if 28 Kf2 Nxf4 29 Ne4 and we don't have a material advantage at all.
if 28 Kh1 Bxc3 29 Rd1 Bd4 and it is Black who has the material advantage.

If 25 Rxf4 Black can free both bishops (and exchange his e-isolani for our d-pawn) with 25 ... e5 26 dxe5 Bxe5

[quote]despite the material advantage we gain.[/quote]... or not.

IMO our 24 Bf4 is refuted by 24 ... Rxf4.

... and so is my puffed-up opinion of our position.

Oops (Maybe that's why I've never gotten above USCF class B.)

Last fiddled with by cheesehead on 2014-03-20 at 16:35
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Old 2014-03-20, 16:38   #3
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They re-took with the rook: 23 ... Rxf6

Our deadline is [url=http://mersenneforum.org/showpost.php?p=369483&postcount=134]Thursday, March 27 12:40 GMT[/url]

--------------------------------------------------------------------------
[QUOTE=WMHalsdorf;369486]I didn't see any analysis for 24. Bf4 Rxf4[/quote]Thank you for that reminder! I see that I'd not yet posted that, or yet looked at it more than a move.

[quote]which opens up the center in what appears to favor Black more than us[/QUOTE]Yes, it does.

If 25 gxf4 Nxd4 then (speculation) if 26 Ne3 bxc3 27 bxc3 Ne2+ and now:
if 28 Kf2 Nxf4 29 Ne4 and we don't have a material advantage at all.
if 28 Kh1 Bxc3 29 Rd1 Bd4 and it is Black who has the material advantage.

If 25 Rxf4 Black can free both bishops (and exchange his e-isolani for our d-pawn) with 25 ... e5 26 dxe5 Bxe5

[quote]despite the material advantage we gain.[/quote]... or not.

All this refutes our 24 Bf4.
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Old 2014-03-20, 16:40   #4
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[B](Go to bottom of post for clean reformatted list!)[/B]

Here is the current move 24 candidate list, merging posts #29, 30, 32 and 33 of the White 23 thread with posts #1 and 2 of this thread:

[strike][B]A)[/B] If [B]23 ... Bxf6[/B]

[B]A1) 24 Ne4[/B]
If 24 ... Nxd4 25 Nxf6+ and 26 cxd4 (defuses the d4 fork-threat)

[B]A2) 24 Bxh6[/B]
If 24 ... Rh8 25 Rxf6 Rxh6 26 Ne3 and we're a pawn up, plus threaten to win more, but must watch out for ... bxc3 and ... Rb2 etc. counterplay. Also must still watch for d4 fork-threat if there's no bishop swap.

- - -

[B]B)[/B] If [B]23 ... Rxf6[/B][/strike]

[B]B1) 24 Rc1[/B] (removes rook from d4 fork-threat, can directly capture c4 in some lines, can support our N/c5 in some lines) Needs analysis <==

[B]B2) 24 Re1[/B] (avoid rook swap, attack isolated e6-pawn in order to burden the R/f6 with pawn-guard duty. If Black intends to try the d4 fork-threat, he first has to move his rook out of the way)

Since this still doesn't deter the d4 fork-threat, we have to consider what Black's rook move-out-of-the-way might add to the d4 threat.
[B]B2A)[/B] If [B]24 ... Rf5 25 Nxe6[/B] (threatens 26 Nxg7) [B]Bxe6 26 Rxe6[/B] (threatens 27 Bxc6+) [B]Rc8[/B] leaves us only a pawn up.
If 26 ... Nxd4 27 cxd4 Bxd4+ 28 Be3 (not Ne3 Bxb2) and we're up a bishop for a pawn.
[B]B2B)[/B] If 24 ... Rf7 needs further analysis. <==
[B]B2C)[/B] If 24 ... Rf8 needs further analysis. <==

[strike]B3) 24 Bf4[strike]
24 ... Rxf4 refutes this move.

If 25 gxf4 Nxd4 then
(speculation) if 26 Ne3 bxc3 27 bxc3 Ne2+ and now:
if 28 Kf2 Nxf4 29 Ne4 and we don't have a material advantage at all.
if 28 Kh1 Bxc3 29 Rd1 Bd4 and it is Black who has the material advantage.
If 25 Rxf4 Black can free both bishops (and exchange his e-isolani for our d-pawn) with 25 ... e5 26 dxe5 Bxe5

[strike]B3A)If 24 ... Rb6 25 Bc7 forces a win of the Exchange.
B3B)If 24 ... Ra8
Note: This rook escapes from our dark-square bishop only to place itself in the sights of our light-square bishop, with only the N/c6 as its shield. In other words, Black self-pins his N/c6 (as a coercion of our force, of course) against his R/a8. This has implications for the d4 threat.
Possible followups now include:
B3B1)25 Ne3
(Note that this does not prevent a d4 fork of N/c5 and R/a1.) <==
Here, if Black were to proceed with the d4 threat, he'd simply give away a rook for a pawn:
B3B1A25 ... bxc3 26 bxc3 Nxd4 27 Bxa8 Ne2+ 28 Kg2 and Black is down a rook. More analysis needed <==
B3B1BSpeculation (not careful analysis): 25 ... g5 26 Bc7 (threatening 27 Nxc4 and 28 Nd6++) Ra7 27 Bb6 Ra8 28 Nxc4. If 28 ... Rxf1+ 29 Rxf1 and Black must defend carefully.
B3B2)25 Nf2 (intending 26 Ne4)
(Note that this does not prevent a d4 fork of N/c5 and R/a1.) <==
B3B3)25 Bc7 (Note that this does not prevent a d4 fork of N/c5 and R/a1.) <==
B3B3A)If 25 ... Nd5 26 Bd6 e5 27 dxe5 Rxf1+ 28 Kxf1 Nce7 29 Bxe7 Kxe7 30 Bxd5 and we're up a piece and a pawn.
B3B3BBut if 25 ... Ra7 26 Bb6 Ra8 the d6 retreat is no longer available. If we were further along a BNNB mating path, that might not matter. But 27 Ne3 fits right in here. :) If 27 ... Nd5 28 Nxd5 exd5 29 Bxd5 threatens 30 Rae1+ discomforting Black's king.
B3C)If 24 ... e5 25 dxe5 Rf8 (not ... Rf5 26 Ne3 or ... Rf7 26 e6) 26 e6 (not 26 Ne3 g5) Ra8. Here we can glimpse a checkmate threat via Ne3, Bc7, Nxc4 and Nd6++. However, order is important. Starting with 27 Bc7 does not work: 27 ... Nd5 28 Bd6 Ra7. So the first move would be 27 Ne3

28 ... Bxe6 (to avoid checkmate by guarding c4)
(if 28 ...Rxf1+ 29 Rxf1 Bxe6 and continue as below)
(not 28 ... Ra7 29 Bb6 Ra8 30 Nxc4 threatening mate with 31 Nd6++)
(not 28 ... Be5 29 Bxe5 Nxe5 30 Bxa8)
29 Nxe6 Rxf1+ 30 Rxf1 and Black is down a bishop, with no way to avoid further losses as far as I can see.
E.g., 30 ... bxc3 31 Nxg7+ Kd7 32 Bb6 or 30 ... Bh8 (any other bishop move results in capture) 31 Nf8 (imprisoning black K at e8) with threat of Nxc4-d6++
or
28 ... Ba6 (to avoid checkmate by guarding c4) 29 Ng4 and we're only a pawn up but Black is still in trouble.
B3D)If 24 ... bxc3 25 Bxb8 cxb2 26 Rb1 Rxf1+ 27 Kxf1 Bxd4 28 Bd6.
B3D1)If 25 ... c2 26 Bc4 cxd1/Q 27 Raxd1 and we're up a rook for a knight.
B3D2)If 25 ... Nxb8 26 bxc3 and we're up a rook for a bishop.[/strike]

- - -

or, [B]reformatted[/B]:

[B]24 Rc1[/B] (removes rook from d4 fork-threat, can directly capture c4 in some lines, can support our N/c5 in some lines) Needs analysis <==

[B]24 Re1[/B] (avoid rook swap, attack isolated e6-pawn in order to burden the R/f6 with pawn-guard duty. If Black intends to try the d4 fork-threat, he first has to move his rook out of the way)

Since this still doesn't deter the d4 fork-threat, we have to consider what Black's rook move-out-of-the-way might add to the d4 threat.
If 24 ... Rf5 25 Nxe6 (threatens 26 Nxg7) Bxe6 26 Rxe6 (threatens 27 Bxc6+) Rc8 leaves us only a pawn up.
If 26 ... Nxd4 27 cxd4 Bxd4+ 28 Be3 (not Ne3 Bxb2) and we're up a bishop for a pawn.

If 24 ... Rf7 needs further analysis. <==

If 24 ... Rf8 needs further analysis. <==

Last fiddled with by cheesehead on 2014-03-20 at 16:49
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Old 2014-03-22, 06:05   #5
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I think I may have been overlooking some reasonable move 24 candidates because of mixups.

For instance, we've analyzed [B]Ne4[/B] only in the context of 23 ... Bxf6, [U]not [B]23 ... R[/B]xf6[/U].

So, I'm adding to the move 24 candidates list:

[B]24 Ne4[/B] moves one potential d4-fork target off the c5-g1 diagonal, chases the rook, threatens Nd6+ but I haven't found any line that forces any advantage for us. <== needs more analysis
(If 24 ... Rxf1+
If 25 Kxf1, two potential d4-fork targets are no longer threatened. If 25 ... Nf5 26 Nd6+ Nxd6 27 Bxc6+ forces a knight swap, but if 27 ... K-moves 28 Bf4 pins knight against rook, but I can't find a way to exploit that. If 27 ... Bd7 we either bishop-swap or 28 Bf3.
If 25 Bxf1 we could follow-up with Bxc4, Nf2-g4 or Ne3.)

[B]24 Be3[/B] guards against the d4-fork threat. LaurV thinks it's "weak", but negating the d4-fork threat is important. Do we want to wait until after ... Bxd4+ to play Be3? <== needs more analysis

We can be more aggressive, but if that aggression doesn't deter the d4-fork, it threatens us with losing a piece or rook.

Last fiddled with by cheesehead on 2014-03-22 at 06:18
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Old 2014-03-22, 15:38   #6
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As it is now, the d4-fork threat will win one of our pawns (via 24 ... bxc3 25 bxc3 Nxd4 and we can't afford to capture the knight) if we do not take either:

1) an action ([B]24 Be3[/B]) that stops the d4 threat for now, or

2) an action that immediately moves one of the three fork targets (N/c5, R/a1, K/g1) off the c5-g1 and a1-d4 diagonals, [U]and[/U] assures that either:
we can move another target off before it's forked,
or
we prevent (not just block) the fork's check on our king.

E.g., 24 Ne4 suffices. If 24 ... Rxf1+, 25 Kxf1 moves another target off its corresponding diagonal, leaving only the R/a1. If 24 ... R-other-move, then we can move either the R/a1 or the K/g1 off its corresponding diagonal. Or we can interpose with 25 Be3 or Ne3, so that we could afford to capture cxd4 after Nxd4 because the subsequent Bxd4 would not give check, allowing us to move the R/a1.

24 Rc1 (or Ra2) also suffices. If 24 ... Rxf1+, 25 Kxf1 moves another target off its corresponding diagonal, leaving only the N/c5. If 24 ... R-other-move, then we can move either the N/c5 or the K/g1 off its corresponding diagonal. Or we can interpose with 25 Be3 or Ne3, so that we could afford to capture cxd4 after Nxd4 because the subsequent Bxd4 would not give check, allowing us to move the R/a1.

If 24 Rxf6 Bxf6 then only 25 Be3 suffices to prevent losing our d-pawn. If 25 ... Nxc4, then
26 cxd4 and Black will probably not sacrifice a bishop for the d-pawn after already having sacrificed a knight-for-pawn, or
26 Bxd4 and if 26 ... Bxd4+ 27 cxd4

24 Re1 does _not_ suffice to save our d-pawn. If 24 ... bxc3 25 bxc3 R-f5/f7/f8 then after 26 ... Nxd4 the knight still cannot be captured, or else 27 ... Bxd4 forks with check.

So, if we don't want to lose a pawn by force, our candidate moves are:

[B]24 Be3[/B]
[B]
24 Ne4[/B]
[B]
24 Rc1

24 Ra2 [/B](also prevents losing the d-pawn for nothing) If 24 ... b3, then Black gives up the d4-fork material-win threat because we can afford to capture the knight after 25 ... Nxd4: 26 cxd4 Bxd4+ 27 Be3.

Now, in some lines Black can sacrifice a knight for two pawns anyway, and may consider that worthwhile. So, which candidate also prevents that (i.e., which candidate(s) not only prevent(s) Black from using the d4-fork threat to win material outright, but also prevents Black from getting two pawns for a knight sacrifice on d4?)

(In each of the following cases, Black can interpolate with ... bxc3 bxc3 before Nxd4, with no change in material balance at the end.)

[B]24 Be3[/B] does. If 24 ... Nxd4 25 cxd4 or Bxd4 limits Black to getting only a single pawn for the Nd4 sacrifice.

[strike][B]24 Ne4[/B][/strike] cannot. If 24 ... Rxf1+ 25 Kxf1 Nxd4 26 cxd4 Bxd4 and Black has two pawns for the knight.
[strike][B]24 Rc1[/B][/strike] also cannot. Just as after 24 Ne4, 24 ... Rxf1+ 25 Kxf1 Nxd4 26 cxd4 Bxd4 and Black has two pawns for the knight.
[strike][B]24 Ra2[/B][/strike]also cannot. Just as after 24 Ne4 or 24 Rc1, 24 ... Rxf1+ 25 Kxf1 Nxd4 26 cxd4 Bxd4 and Black has two pawns for the knight.

- - -

So,as far as I can see, the only move 24 that prevents Black both from winning material and from getting two pawns for a knight sacrifice is:

[B]24 Bd3[/B]. Admit our move 22 mistake, and get on with playing the best move in the position in which we find ourselves.

- -

My vote (unless someone can refute my analysis above):

24 Bd3 - 5
else - 0

Last fiddled with by LaurV on 2014-03-23 at 03:58 Reason: repaired three misspeled "strikes"
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Old 2014-03-22, 21:20   #7
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You forgot about doing 24. Rxf6 Bxf6 first. Some move that are not playable may become playable such as 25. Bf4 and 25. Ne4
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Old 2014-03-23, 06:36   #8
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Oops.

[QUOTE=cheesehead;369600]
So,as far as I can see, the only move 24 that prevents Black both from winning material and from getting two pawns for a knight sacrifice is:

[B]24 [/B][B][strike]Bd3[/strike]Be3[/B]. Admit our move 22 mistake, and get on with playing the best move in the position in which we find ourselves.

- -

My vote (unless someone can refute my analysis above):

24 [strike]Bd3[/strike]B[B]e[/B]3 - 5
else - 0[/QUOTE]
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Old 2014-03-23, 07:05   #9
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I am SO glad that you folks don't have the same blind spots that I do!

[QUOTE=WMHalsdorf;369615]You forgot about doing 24. Rxf6 Bxf6 first.[/QUOTE]Technically, I didn't forget, but my posted explanation[QUOTE=cheesehead;369219][strike]24 Rxf6[/strike] (does not deter the d4 threat; indeed, actually assists it)[/QUOTE]was terse, easily overlookable, and [u]based on flawed analysis (i.e., [B]WRONG[/B])[/u].

[quote]Some move that are not playable may become playable such as 25. Bf4 and 25. Ne4[/quote][B]You are correct, sir![/B]

25 Bf4 was refuted only by 25 ... Rxf4.

25 Ne4 threatens to take the B/f6 with check, so then 25 ... Nxd4 26 Nxf6+ becomes a loser for Black.

However, as you point out ("may become playable") we need to look closer. For instance, after Rxf6 Bxf6 our King is still on the checkable-from-d4 diagonal rather than f1.

Furthermore, "loser for Black" still admits the deliberate sacrifice of the [i]dark-square bishop[/i] (rather than the N/c6) for two pawns: 25 Ne4 Bxd4+ 26 cxd4 Nxd4 and that knight could be troublesome.

Both need more analysis, which I'll do right now ... Stay tuned.
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Old 2014-03-23, 08:49   #10
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Hmmm... this will take a while.
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Old 2014-03-23, 10:37   #11
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This move is impossible to decide! All moves have good or bad. In a real game now (after having all this analysis, and not before!) I would play Bf4. I think is the most aggressive, and block the rook exchange quite well. I know it has some bad part, as cheesehead already has shown. I consider that Rc1 and Re1 are 'safe' moves, but not so aggressive.

I consider other moves 'weak' in this position, we have some advantage that we have to maintain, and all the other moves either are very bad, or are "still ok", but give back (most of the) advantage we had. For example Be3, after they exchange the pawns in c3 (our bishop left the guard down there) and the rooks in f1 (which we must take), the board looks "empty", they have the offensive (sente), and I don't believe we can get more than a draw there.

I will look more this evening into it.

Last fiddled with by LaurV on 2014-03-23 at 10:37
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