Strategy--Checker play

Forum Archive : Strategy--Checker play

Jacoby rule consideration

From:   Ron Karr
Date:   19 November 1996
Subject:   Re: Whats the best strategy for this position?

Kit Woolsey wrote:
> MJR wrote:
> > Money game, cube in center:
> >
> > -------------------------------
> > | O O O O O O | | - - - - - X |
> > | O O O O O O | |           X |
> > |         O O | |           X |
> > |             | |           X |
> > |             | |           X |
> > |             | |             |
> > |             | |             |
> > |     X X X X | | X           |
> > | - O X X X X | | X - - - - - |
> > -------------------------------
> >
> > Does X ever want to slot the 8 point, or hit loose?
> > How to play 3-2 or 4-1.
> X never wants to slot the eight point.  The one thing he can't risk is to
> have O escape with a hit.  While X has to take some positive action to
> drive O's checker back since O is ahead in the race, slotting the eight
> point is not the right idea.  If X doesn't gut lucky and roll a joker to
> build the eight point, he will plan to hit loose on the two point.
> However, he cannot afford to break his five-prime to do this -- that
> makes it too easy for O to escape if he hits back.  So with 3-2 or 4-1 X
> has no choice but to bring builders down.

Kit is correct that slotting the 8 point with a 3-2 or 4-1 is normally
wrong.  For example, Jellyfish shows the equity from 13/8 as -.119 while
the equity from 13/9 13/12 is +.072.

However, I think slotting the 8 point is in fact correct under the
conditions stated (money game, cube in the middle).  The reasons:

If X slots and O hits with a 6, O has now lost his market by a ton and
has significant gammon chances, so in a match, he would play on for
the gammon.  However, in a money game (as this problem was stated),
the Jacoby rule is in effect.  So after hitting O must settle for a
single point by doubling.  Therefore there's no "extra" cost to X to
getting hit. And O is not strong enough to double BEFORE hitting in
order to activate gammons.

If X alternatively brings 2 builders down, O's sixes are pretty good
anyway.  4 numbers hit a blot and 1 number (66) runs to safety, thereby
winning with the cube.  The other 6 sixes leave X roughly a double shot
to hit back.  Let's say that of those, X wins 4 games and O wins 2.  So
only wins an extra 4 games or about 11% by making the safer play.

What's the gain from slotting?  When O doesn't hit, X now has an
extremely efficient cube turn, since he has many numbers that either
make the 8 point or hit on the 2.  Jellyfish shows X's cubeless equity
as around .52.  With cube leverage, this should be a take for O, but it's
close to a pass.  In other words, X can convert around a 75% chance of
winning to almost 100% by doubling.

Suppose X doesn't slot and O doesn't roll a 6.  Now X is a favorite, but
not nearly enough to claim.  He will still have to make the 8 point, or
hit on the 2 point and not get hit back, in order to win.  Meanwhile O
continues to have escaping chances.  Jellyfish says X's equity after
13/9 13/12 is .365.

So is the gain from being able to almost claim with the cube after a
slot worth the extra 11% chance of being hit immediately?  I think so.
But only because gammons won't count against X.  If the Jacoby rule were
not in effect, or the cube had already been turned, the slotting play
would be wrong.

The concept here:  it's worth taking a risk that increases the value of
the cube to you.  If the risk succeeds here, X gets tremendous value
from doubling; if the risk fails, O gets no value from the cube.

Did you find the information in this article useful?          

Do you have any comments you'd like to add?     


Strategy--Checker play

Avoiding major oversights  (Chuck Bower+, Mar 2008) 
Bearing off with contact  (Walter Trice, Dec 1999) 
Bearing off with contact  (Daniel Murphy, Mar 1998)  [Long message]
Blitzing strategy  (Michael J. Zehr, July 1997) 
Blitzing strategy  (Fredrik Dahl, July 1997) 
Blitzing technique  (Albert Silver+, July 2003)  [GammOnLine forum]
Breaking anchor  (abc, Mar 2004) 
Breaking contact  (Alan Webb+, Oct 1999) 
Coming under the gun  (Kit Woolsey, July 1996) 
Common errors  (David Levy, Oct 2009) 
Containment positions  (Brian Sheppard, July 1998) 
Coup Classique  (Paul Epstein+, Dec 2006) 
Cube ownership considerations  (Kit Woolsey, Apr 1996) 
Cube-influenced checker play  (Rew Francis+, Apr 2003)  [GammOnLine forum]
Defending against a blitz  (Michael J. Zehr, Jan 1995) 
Estimating in volatile situations  (Kit Woolsey, Mar 1997) 
Gammonish positions  (Michael Manolios, Nov 1999) 
Golden point  (Henry Logan+, Nov 2002) 
Hitting loose in your home board  (Douglas Zare, June 2000) 
Holding games  (Casual_Observer, Jan 1999)  [Long message]
How to trap an anchor  (Timothy Chow+, Apr 2010) 
Jacoby rule consideration  (Ron Karr, Nov 1996) 
Kamikaze plays  (christian munk-christensen+, Nov 2010) 
Kleinman Count for bringing checkers home  (Øystein Johansen, Feb 2001) 
Late loose hits  (Douglas Zare+, Aug 2007)  [GammOnLine forum]
Mutual holding game  (Ron Karr, Dec 1996) 
Pay now or pay later?  (Stuart Katz, MD, Nov 1997) 
Pay now or pay later?  (Stephen Turner, Mar 1997) 
Pay now or play later?  (Hank Youngerman+, Sept 1998) 
Play versus a novice  (Courtney S Foster+, Apr 2004)  [GammOnLine forum]
Playing doublets  (Grunty, Jan 2008) 
Playing when opponent has one man back  (Kit Woolsey, May 1995) 
Prime versus prime  (Albert Silver+, Aug 2006)  [GammOnLine forum]
Prime versus prime  (Michael J. Zehr, Mar 1996) 
Saving gammon  (Bill Riles, Oct 2009) 
Saving gammon  (Ron Karr, Dec 1997) 
Splitting your back men  (KL Gerber+, Nov 2002) 
Splitting your back men  (David Montgomery, June 1995) 
Trap play problem  (Brian Sheppard, Feb 1997) 
When in doubt  (Stick+, Apr 2011) 
When to run the last checker  (Stick Rice+, Jan 2009) 
When you can't decide  (John O'Hagan, Oct 2009) 

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