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Archive for the ‘Oldmanc backstepped F’ Category

Oldmanc (backstepped) F, close-X line 1

Posted by nand on April 1, 2010

Here’s a line I’ve used a lot lately with a fair amount of success.  I think it’s probably flawed but because the flaw comes in the midgame not early on it takes a very shrewd or lucky violet player to see the problems here.

If violet blocks on the bottom this is an easy win for orange–play N on the top (F12rrur) & violet’s defence crumbles. The tricky part comes if violet instead blocks with V5(H12uurr) or T5(H12uur), because the blocking in orange’s area is really awful–you basically end up giving away at least a 4-piece &/or being forced to use the I1. That said, I think this line is worth exploring further. Orange’s continuation on the bottom is of course Z5 or T5–I think Z5 is better but have not conclusively proven this.

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Studies in backstepped F #5

Posted by nand on June 23, 2009

Continuing our examination of orange X-up responses (which, again, I think aren’t all that good, but can still be very tricky for violet to win if orange is savvy)…. here’s a look at the main line for orange and violet.

Tricky but not hopeless for orange

Tricky but not hopeless for orange

The main problem with this particular opening is that it’s susceptible to “quasi-mirroring”: viz., orange keeps playing roughly “equivalent” moves (if violet plays a long hanging piece, then orange plays a long hanging piece; if violet plays a kiss move, then orange plays a kiss move), and even if they aren’t exact mirrors the results are usually nearly a tie. So violet must find a way to (1) create a decisive advantage and (2) do it before orange gets within striking distance of the vulnerable left bottom corner of violet’s N (if orange is permitted to cut that off, then orange obtains most or all of the left bottom corner, which probably means an orange win).

This game shows one way of trying to stop the circling & create a violet advantage by pushing orange away from the vulnarable N while maintaining violet attacks on both fronts. Mike Yosuke first showed me the violet L5 move here. Its power is that orange cannot BOTH block the right AND attack, since the only move that will cut off the violet L5 is orange I5 (and to do so would be to permit violet to attack on the left on the following turn).

That said, violet has a very precarious position on the bottom, as the nicer long pieces (Y, N, L5) are now all gone and violet has few felicitous ways to defend the bottom while maintaining control over the bottom left. As you can see from the following game, simply ceding the bottom left corner results in a tie:

64-64 tie. Violet I4 is obviously too cautious.

64-64 tie. Violet I4 is obviously too cautious.

Moves:
1. F – X
2. X – W
3. N – Y
4. L5 – N
5. Y – L5

Violet Y may be turned with the knob on the left rather than the right. If this is done, then I think orange must play I4 or I5–the key is to NOT kiss, as it’s important not to give violet ANY easy way to grab the bottom left corner.

6. W – Z5

Orange Z5 here is the maximum headache I could think of for violet: it makes a credible threat (to block off the bottom left corner & get a paw on violet’s N) and cannot be blocked by any single move with the exception of violet I4. (Violet I5 would give orange a 1-T4-I3 series of holes: disastrous.) — All that said, it’s not entirely clear to me that violet need block it, rather than blocking off the top. But for the sake of this analysis let’s look at what happens if violet blocks….

7. I4 – F

NOT T5 or anything else that could be blocked with a piece that would also simultaneously dispose of the leak off orange X. Orange needs to keep this leak in play….

8. T5 – 1
9. Z5 – I2
10. I3 – V5
11. P, and the rest is packing.

The result: a 64-64 tie. Quite nice for orange. So, the question is: can violet do better by ignoring the orange Z5 & proceeding with the attack on top? Tune in to the next episode to find out….

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Studies in backstepped F #4

Posted by nand on June 23, 2009

I’ve been trying to be thorough with this opening, as I wish to leave no avenue unexplored. So I’m starting with what I consider to be the weakest lines first, where orange plays X up and then plays below rather than wrapping above. (In general I think that all the wrap-below options are bad for orange.) Here is what happens if the orange line I discussed in the previous post in this series — X-Y-N — is not immediately blocked by violet.

Violet 61 - Orange 56. This is cautious play for violet yet it's a 5-point win.

Violet 61 - Orange 56. This is cautious play for violet yet it's a 5-point win.

Moves:

1. F – X
2. X – Y
3. N – N
4. Z5 – W

Two notes here. 1) I picked orange Z5 because it’s the most difficult move for violet to block (because in the following move, as we’ll see, violet decides to block, so I wanted to make life difficult for him) and because I think orange F is more useful for defense on the bottom. If someone can show me a better move here or in the following steps I’d be interested to know.

2) Violet W is key: violet Z5 looks as good or better, but it’s actually a terrible mistake. As we’ll see, we need the Z5 for the block on top, & violet W on the bottom also keeps vulnerable corners away from orange.

5. Z5 – L5

I wanted to see what happens if violet plays defensively from this point onwards. Surprisingly, the answer is that — even though it looks like the board is split nearly evenly — violet has a quite decent win in his pocket. The key from this point is for violet to hang on to the Y, as the Z5-Y combo is what seals the top (with L4, T4, or V3 equally good for capping it off)

6. L4 – F
7. T5 – I2
8. Y – I1
9. V3 – W and the rest is packing.

Final score 61-56 for violet — pretty good showing. I may have missed a slightly better packing.

Unless someone can show me a variant line I will assume that the X-Y below line for orange is a washout, & move on to other lines.

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Studies in backstepped F #3

Posted by nand on June 19, 2009

In my previous post I’d started to explore what happens if orange plays X-up then circles beneath rather than above. My general feeling is that this is bad for orange but it cannot be instantly ruled out. Orange L5 on move 3 is a bad response, as we saw, since violet can block it with impunity & win handsomely. Orange N, on the other hand, cannot be blocked without violet getting into serious trouble. With ideal packing on both sides, I believe violet still wins by 1 point: here’s my packing:

Violet 61, Orange 60

Violet 61, Orange 60


If there’s an improved packing for either side I’d like to know, as it obviously makes a huge difference in a game this close to a tie.

Moves:

1. F – X
2. X – Y
3. N – N
4. W – Z5
5. P – 1
6. L5 – Z4
7. 1 – V3
8. I2 – L4 and the rest is packing

Obviously on move 4 violet must ignore orange N & instead wrap around the right with W or Z5. I think those lines do not obviously favour either side, but need to investigate further.

The other question here is whether violet N on move 3 is good. I can’t see any other obvious move, but I may be wrong.

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Studies in backstepped F #2

Posted by nand on June 18, 2009

This is the opening I’m currently exploring a lot, as I find it very slippery. My basic feeling is that it’s not a very good opening once analyzed carefully, but it’s got enough complexity to it that it can really throw some players for a loop (including me).

My general feeling is that orange’s worst option is X up, & that trying to go underneath violet X on move 2 rather than over the top is also bad. But, again, it’s never exactly straightforward with this opening. Anyway, I’m going to pick away at it slowly, so let’s start with lines that are obviously bad for orange, before I get to ones that may favour orange.

Final score violet 65, orange 58

Final score violet 65, orange 58

Moves:

1. F – X
2. X – Y
3. N – L5

I’m not sure that violet N is good, but I’m very sure that orange L5 is a bad response to it. At this point violet has no particular reason to continue circling: he can take a stand & count on grabbing enough points to win.

4. Z5 – Z5

Violet Z5 rather than T5: normally I’d want the T5 because of the extra corner in orange’s area, but in this case (1) this is going to be a packing game and violet needs all the extra space and corners within his own area that he can get, and (2) the Z5 is plenty threatening on its own, as orange has no clean way to block it without creating further leaks.

5. P – 1
6. L5 – P

This is my best solution to the problem of how to staunch the leak off violet Z5. If violet plays I3 or I4, then orange I4 can cut across it easily.

7. I5 – U … and the rest is packing.

Possibly there is a better solution to the packing for orange; but I’m sure that the violet packing is optimal.

So: a 7-point loss. Clearly a bad line for orange. Next question is whether it’s stronger if orange L5 is replaced with a different move (like Y or N or W)…

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Studies in backstepped F #1

Posted by nand on May 24, 2009

The "delayed" F opening, take 1

The "delayed" F opening, with a double-block

The usual idea with this opening is for violet to wrap N around orange X on move 3 (killing a bunch of corners) & then keep squeezing. There are basically two approaches for violet to this opening (& to many others): circling (i.e. both players keep moving counterclockwise) and blocking (when violet stops the circling with a block — often with a double-block by doing the same thing on the next turn). This game is an example of a double-block, with violet L5 and N.

I have a general theory about this opening: if orange loosely “mirrors” it (i.e. plays a piece on the opposite side from violet rather than blocking, & roughly matching violet’s level of aggressiveness — i.e. match a kiss with a kiss, a hang with a hang) then it’s very hard to lose by a lot, & in fact one can often eke out a win or tie. It’s a 50-50 type of game as long as orange doesn’t panic… I think.

Anyway, here’s one example, caught in the wild. I’ll get around later to discussing the line if violet puts Y or N on top of orange X on move 3. The key here is that orange F creates a nasty trap for violet, because there’s a classic unblockable 1-2 series of holes on the top of violet F. Violet’s strategy may be at fault here — I’m pretty sure violet Y is a mistake, as it’s necessary to close the bottom side (e.g. with T5) to avoid getting the return threat created by orange L5.

Here is the move order:

  1. F – X
  2. X – N
  3. L5 – F
  4. N – Y
  5. Y – L5
  6. Z5 – I5 …. and the rest is self-explanatory.

If violet blocks off the bottom attack then it looks better for violet:

This time violet cuts off the bottom

This time violet cuts off the bottom

I’m pretty sure it’s disaster for orange to block V5 below immediately. Violet would simply play Z4 or P up top to both block the attack off orange Y & staunch the dangerous leak off orange F. Here’s one possible line (probably not ideal) that results in a minor win for violet.

One possible line: 4-pt win for violet

One possible line: 4-pt win for violet

Maybe this would be a point or two better if orange plays L5 above, then T5 rather than L5 in the bottom (I think violet would be unlikely to block the T5 in favour of defending top left), then U and O4 to fill the bottom, Z4 rather than W to fill the hole, & repack accordingly… Choices, choices. (I just tried that — the results are 65-61, the same difference.)

To explore this line more thoroughly we’d need to check what happens with various violet blocks other than T5, & also the possibility if violet plays L4 wrapping around the bottom of orange X. Orange could play L5 not Z4 on top, threatening Z5-I2-I4 down the side of violet’s pieces… the problem here being that if orange really went through with this plan, in the interim violet could make serious (hole-less) grabs for space on the right.

*****

Postscript
I’m not entirely sure how the game works out if orange plays Y up: but here’s one winning line for orange. Possibly N for violet on top would do better than Z.

Not so good for F... maybe Y would be better than V5 below?

Final score 66 for orange, 60 for violet. Maybe Y would be better than V5 below?

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