Tuesday, September 3, 2013

Chess960: Competition to find the SP with the highest number of viable first moves

Discovered a start position SP today that has a ridiculous amount of viable first moves options! More than standard chess in fact, fifteen in total. The absolute maximum number of first moves in some Chess960 starts is 21, but usually a large number of those can be ridden off because they are possible but theoretically too weak.

So here's the challenge.

See if you can find an SP that has more viable opening moves than this one:

SP491: 15 viable first moves
  1. a3 - yes because it enables Qa2 developing the queen
  2. a4 - yes because it enables Qa3 developing the queen
  3. c3 - yes because it defends against Bh8 and allows d4
  4. c4 - yes because it claims some center and can be supported by d3
  5. d3 - yes because it develops a bishop
  6. d4 - yes because it develops a bishop
  7. e3 - yes because it allows Ne2/c3
  8. e4 - yes because it claims some center and allows Ne2/c3
  9. f4 - yes because it develops a bishop, controls g5 and threatens f5
  10. g3 - yes because it develops a bishop
  11. g4 - yes because it develops a bishop and is supported by a rook
  12. h4 - yes because it takes control of g5, threatens h5 and allows Nh2/f3
  13. Nb3 - yes because it controls d4
  14. Nd3 - yes because it enables rapid castling
  15. Ne3 - yes because it is flexible and developing
After a depth 24 search, Houdini-3 thinks that the variation in score between the best and worst first moves in that list is +/- 0.1 which is tiny. Realize that favoring a quick development of the corner bishop to attack the queen is not especially powerful and can be handled without problems.

In contrast, standard chess has at the very most 13 viable first moves but the variation in score is much bigger at +/- 0.43.

SP491 has a unique set of conditions with the queen in the corner allowing more options and a pair of knights that can be developed in a variety of ways. Also, the rooks support pawns that can be played out effectively. The only thing holding it back is less than optimal ways to develop the bishops. That opens the door for an SP which could possibly hit 16 viable first moves.

From my experience, I think SP491 could take the all time record. Prove me wrong!


  1. Great post Harry, very interesting and informative.

    Also, this kind of evidence suggests that opening variety would be significantly greater in a SP491 world than in the traditional SP518 world.

    When I understood what this post was about, I hoped that SP491 was a setup that had...
    (A) no corner bishops, and
    (B) both white knights on the same shade of square as each other, and
    (C) a larger probability of castling on the a-wing (meaning like O-O-O or "castling long" in traditional chess; where the king arrives on the c-column).
    However, SP491 has only (C) of these above attributes.

    So I wonder which setup that does have all three of these attributes would have the most viable first moves.

    It is slightly disappointing that SP491 seems to give White a bigger than average advantage over Black, according to...


    Also, unfortunately the draw rate for SP491 is bigger than average.


  2. Thanks for that link to CCRL Gene didn't know they broke it down by individual SP.

    The draw/win rate in SP491 seems very close to SP518 (standard chess)
    SP491: 108 games draws 19.4% white wins 56.9%
    SP518: 149 games draws 20.1% white wins 55.0%

    Computer choices for SP491:
    Nb3: 14 games draws 21.4% white wins 35.7%
    Nd3: 8 games draws 12.5% white wins 87.5% (huge white bias!)
    d3: 14 games draws 28.5% white wins 42.9%
    d4: 12 games draws 33.3% white wins 33.3% (amazing balanced stat!)
    Ne3: 15 games draws 20% white wins 40%
    f4: 7 games draws 0.0% white wins 28.6% (huge bias to black!)
    g3: 18 games draws 22.2% white wins 55.6%
    g4: 17 games draws 6% white wins 52.9% (low draw rate!)
    (three other games just noise)

    One interesting thing about this SP is that because the bishop and queen are in the corner, there is no compulsive reason to necessarily take control of the center. This could actually be part of the secret as to why there are so many viable first moves including pawns moves on the flanks.

    So the next thing to study are why the extreme stats noted for Nd3, d4, f4, g4?

  3. Mark Weeks shares his thoughts on SP491 here: