HDTenEightyP/NetNews huggingface dataset:
From: hyatt@cis.uab.edu (Robert Hyatt)
Subject: Re: "Solvability" in Chess
Organization: University of Alabama at Birmingham
Date: Wed, 30 Sep 1992 01:30:27 GMT

In article <717712154.93@mailbox.bison.mb> edward.m.hummel@mailbox.bison.mb.ca (edward.m.hummel) writes:
>Organization: AT&T
>
>In article <lc47bsINNohc@yoakum.cs.utexas.edu> varvel@cs.utexas.edu (Donald A. Varvel) writes:
>>1. I'll chime in with the people saying the requirement to *claim*
>>   a draw by 50 move rule or 3-fold repetition is a red herring.
>>   The example of both players shuffling knights back and forth and
>>   neither claiming a draw is beside the point.  The question is
>>   whether the opening position is a win, loss, or draw *with best
>>   play*.  After enough knight-shuffling, it's at best and at worst
>>   a draw, since either side *can* claim one.  These two rules
>>   (and actually 3-fold repetition is sufficient) make the game finite.
>
>I think this argument rest on the assumption that chess is a zero sum game.
>How do you prove that?  Suppose the value of an infinite game is less than
>a draw for each player (but more than a loss), then neither player
>would choose a draw *with best play*.
>
> * Origin: The Electronic Mailbox (1:348/7.0)
>

Chess is clearly a zero=sum game game.  Either white wins and black loses,
black wins and white loses, or the game is a draw.  infinite games are not
possible with the current rules, namely the 50-move rule.  It is not possible
to obtain any other outcome except to terminate the game early.  In that
case, the chess clock still makes it a win or loss (or draw if insufficient
material remains)  How can you consider the game anything else?  How can the
game be infinite? 


-- 
!Robert Hyatt                    Computer and Information Sciences   !
!hyatt@cis.uab.edu               University of Alabama at Birmingham !
From: tennis@ziff.com
Newsgroups: rec.games.chess
Subject: Re: DEEP THOUGHT II vs KASPAROV
Date: 24 Sep 92 17:56:15 EDT
Organization: Ziff-Davis, Medford MA

In article <1992Sep22.050445.6453@cs.ubc.ca>, kvdoel@cs.ubc.ca (Kees van den Doel) writes:
> In article <1992Sep21.211632.15541@ucsu.Colorado.EDU> cuffell@spot.Colorado.EDU (CUFFELL TIMOTHY MICH) writes:
>>Sorry.  Math time.  Everyone seems to be making these impossible claims
>>about computer search spaces.  50 moves in the future?  No.  Assume there are
>>twenty legal moves at any given point.  (This is based on actual research, not
>>a number I pulled out of my hat.)  That means there are 2^50 (sic), or 10^65 
>>positionsto evaluate.  
> 
> It's math time indeed. 1 move = 2 plies so the number you are thinking of is
> 20^100 = 10^130. But not all positions need to be evaluated (alpha-beta 
> pruning) which brings the average branching factor down to about 6. So
> then only 6^100 = 6*10^77 positions need to be looked at.
> 
> Could it be possible that there is a still better algorithm to be
> invented? Can it be shown that this is impossible?
> 
> --Kees
> 
> 
> 

Blessed Bovine! 6*(10^77) is a HYOOOMONGOUS number! In fact this number is
larger than the number of electrons in the universe, I believe!  It looks
something like this:

60000000000000000000000000000000000000000000000000000000000000000000000000000

But, since it is math time, here is my best guess:

Divide the above number by the
number of positions you can do in a second. Lets say this value is 1e6, which
sounds pretty high.  So you have to spend 10e71 seconds to solve chess. With
about 3e7 seconds in a year, you will have to wait 10e64 years for a solution.

Assuming I am off by a factor of 10000 to the conservative side, you will only
have to wait 10^60 years.  The sun will have long since burned out by then.
In fact, the universe is only about 15 billion (15e9) years old.

I think chess is unsolvable given the above parameters.

And as far as pulling numbers from a hat goes, your 6 possible (reasonable)
moves may or may not be correct, but you did pull it from your hat. ;) But
it could be 6, could be 10. Does not matter, you will have a power failure
before you have finished. :)

Tony Ennis
From: cracraft@rice-chex.ai.mit.edu (Stuart Cracraft)
Newsgroups: rec.games.chess
Subject: Converting Fide algebraic to Computer algebraic
Date: 3 Oct 92 05:12:48 GMT
Organization: MIT Artificial Intelligence Lab


Hi,

I have several megabytes of Fide algebraic moves I want to convert
to computer algebraic (e.g. Nf3 => g1f3).

Does anyone have some software that can do this?

The purpose is simply to enlarge an opening book for a non-commercial
ratings test against net players, the result of which will be announced
on info-gnu-chess@prep.

Thanks,
Stuart
From: Bruce.Harper@mailbox.bison.mb.ca (Bruce Harper)
Newsgroups: rec.games.chess
Subject: Re: Fischer-Spassky game 15: bewilderment
Date: 5 Oct 92 10:30:01 GMT

Organization: MIND LINK! - British Columbia, Canada

Upon further examination of the end of Game 15, it makes more sense if you
substitute 31...Rxb2 for 31...Kg7.  The game then ends 31.Qd5 Rxb2 32.Qd8+
Kg7 33.Nf5+ gxf5 34.Qg5+ drawn.  I suspect a move was just omitted in the
posting.

(Any views on whether Fischer had to allow ...Bxf3!?)?

 * Origin: The Electronic Mailbox (1:348/7.0)
Newsgroups: rec.games.chess
From: gary@suite.sw.oz.au (Gary Corby)
Subject: 1. g3 Nf6 2. Bg2 d5 3. c4
Organization: Softway Pty Ltd
Date: 29 Sep 92 23:21:49 GMT


Has anybody ever come across an analysis of 
this opening?  What do you think of it?

I've tried playing it several times, treating it
like a reversed Pterodactyl variation of the Modern
Defense.  Without exception every opponent has 
replied 3. ... dc, after which 4. Qa4+ c6 5. Qxc4.
The best line against it however to my mind is 
3. ... Bd7 4. Qxc4 Bc6, directly challenging the 
fianchettoed bishop.


-- 
Gary Corby  (gary@softway.oz.au)
From: fry@zariski.harvard.edu (David Fry)
Newsgroups: rec.games.chess
Subject: F-S II game 13 drawn - moves
Date: 1 Oct 92 22:10:00 GMT
Article-I.D.: husc3.1992Oct1.181001.16002
Distribution: world
Organization: Harvard Math Department



Reuters says: "Fischer missed three changes -- after the 17th, 18th
and 21st moves -- to gain strategic advantage by failing to move
[f2-f3].  This allowed Spassky to regain ground by maneuovering his
knight."

Fischer required that the playing hall be kept dark today, so the hall
is lit only by the stage lights.  The audience has the impression of
being at a movie.

   Fischer Spassky
   (White) (Black)
   1. e4 c5
   2. Nf3 Nc6
   3. Bb5 g6
   4. Bxc6 bxc6
   5. O-O Bg7
   6. Re1 f6
   7. c3 Nh6
   8. d4 cxd4
   9. cxd4 O-O
   10. Nc3 d6
   11. Qa4 Qb6
   12. Nd2 Nf7
   13. Nc4 Qa6
   14. Be3 Qxa4
   15. Nxa4 f5
   16. exf5 Bxf5
   17. Rac1 Rfc8
   18. Na5 Bd7
   19. b3 Rab8
   20. Nc3 Kf8
   21. a3 Nh6
   22. b4 Nf5
   23. Red1 Ke8
   24. Ne4 Rb5
   25. h3 h5
   26. Rd2 a6
   27. Kf1 Rd5
   28. Rcd1 Rb5
   29. Ke2 Be6
   30. Rc1 Kd7
   31. Nc3 Rbb8
   32. Kf1 h4
   33. Ke2 Bf6
   34. Ne4 Bd5
   35. Kd3 Bg7
   36. Rdc2 Rc7
   37. Re1 Rf8
   38. f3 Rb8
   39. Nc3 Bg8
   40. Ne2 Bf7
   41. Bd2 Bf6
   42. Rec1 Rbc8
   43. Nc4 Rb7
   44. Na5 Rbc7
   45. Nc4 Rb7
   Draw agreed.
From: Bruce_Harper@mindlink.bc.ca (Bruce Harper)
Newsgroups: rec.games.chess
Subject: Re: Fischer-Spassky game 15: bewilderment
Date: 5 Oct 92 04:30:01 GMT
Organization: MIND LINK! - British Columbia, Canada
Distribution: world

Upon further examination of the end of Game 15, it makes more sense if you
substitute 31...Rxb2 for 31...Kg7.  The game then ends 31.Qd5 Rxb2 32.Qd8+
Kg7 33.Nf5+ gxf5 34.Qg5+ drawn.  I suspect a move was just omitted in the
posting.

(Any views on whether Fischer had to allow ...Bxf3!?)?
From: elkies@ramanujan.harvard.edu (Noam Elkies)
Newsgroups: rec.games.chess
Subject: Damping the Damiano [Re: mirror, mirror...]
Keywords: Damiano gambit: Petroff 3...Nxe4?!
Date: 29 Sep 92 02:22:36 GMT
Article-I.D.: husc3.1992Sep28.222237.15926
Organization: Harvard Math Department

In article <DUBACH1.92Sep28123155@husc10.harvard.edu>
dubach1@husc10.harvard.edu (joev dubach) writes:
>Now, that isn't very nice.  The Daring Damiano is a perfectly valid,
>dicey opening.  What's your line for 1. e4 e5 2. Nf3 Nf6 3. Nxe5 Nxe4
>4. Qe2 Qe7 5. Qxe4 d6? (? refers to the sentence, not the move :) )

Certainly if Black's play is to be ?'d, d6 is not the problem...
3...Nxe4?! seems to be the appropriate annotation --- not ?? as the
beginner's book would tell you, but not ! as Damiano advocates
would like to believe, either.

>I have played this line in speed and in tournament chess with
>reasonable success.  For more info on it, check out Chess Life,
>sometime a couple of years ago.

As I recall, it ended with the conclusion that, although you have
surprisingly good chances against an opponent convinced that you've
merely fallen into an ancient opening trap, White can remain up a
pawn for no or negative compensation with good play.  Or have new
resources for Black been found?

--Noam D. Elkies (elkies@zariski.harvard.edu)
  Dept. of Mathematics, Harvard University
From: wp01jst1@ucsbuxa.ucsb.edu (John Tomas)
Newsgroups: rec.games.chess
Subject: Re: F-S II game 12 (?): comments
Date: 4 Oct 92 00:39:47 GMT


Methinks Eric is being too generous with ... a5?  I suspect that there
are at least 1000 players in the world who could win the game after
that move.  I can't believe that the player of the Black pieces in that
game has pretensions to be world champion.

Newsgroups: rec.games.chess
From: schiller@whorf(Eric Schiller)
Subject: Re: Endgame Oddity
Reply-To: schiller@sapir.uchicago.edu
Organization: University of Chicago Computing Organizations
Date: Sat, 3 Oct 1992 18:42:29 GMT

In article <1992Oct3.034600.27907@alchemy.ithaca.ny.us>  
cpf@alchemy.TN.Cornell.EDU (Courtenay Footman) writes:
> Here is an amusing position that I reached at the 4th Annual
> SAAWA Upstate Open Chess Tournament.  I was going to
> submit it to "The Guinness Book of Chess Records" until
> I was informed there was no such thing :-).
Yes, there is a Guiness book of Chess Records. Have a copy at home,
but don't remember the publisher offhand. Came out in the 1980s.
--
***** ** *** **** ***** ** *** **** ***** ** *** **** ***** ** *** ****
Eric Schiller                              schiller@sapir.uchicago.edu
Dept of Linguistics, Univ. of Chicago      schiller@whorf.uchicago.edu
                                  
Newsgroups: rec.games.chess,rec.games.go
From: s9874203@titan.ucc.umass.edu (s9874203)
Subject: Re: mirror, mirror on the board...
Organization: University of Massachusetts, Amherst
Date: Tue, 29 Sep 1992 22:20:38 GMT

In article <1992Sep29.133831.1@fnalo.fnal.gov> jpxu1@fnalo.fnal.gov writes:
>In article <1992Sep29.134016.1649@ll.mit.edu>, nates@ll.mit.edu ( Nate Smith) writes:
>> 
>> there is an old story from Go as told by O.Korschelt.  Long ago the best
>> Go players were in china.  there was an arrangement of political cosmetics
>> whereby the Crown Prince of Japan was invited to play against the reigning
>> chimese champion.  the story goes that for years the chinese champion won.
>> then one year the Japanese prince of the time hit upon the idea of playing
>> his first Black stone in the exact center (K10) and then symmetrically made
>> mirror moves of white's, reflected through that stone.  the story also goes
>> that in this manner he actually won, by having the center stone link his
>> armies together at the end.  comments were made that - although highly
>> unlikely to be true - the level of play in china must not have been too
>> strong yet (remember Go is 4000 years old and this was from way back in
>> those early years, supposedly), for an easy strategem can be found to
>> foil this mirror.
>> 
>> cheers,
>> 
>>  - nate
>
>You are wrong nate.  There is no way to stop it. That's what the komi for.
>
>And if you watched the very old chinese games, there were 4 stones before
>
>the game starts.   That actually is  another way to break the symestry.
>
>--jpx 

You are wrong, jpx.:-) There IS a way for white to kill black in the
middle IF black exactly mirrors white's move. Anyone wants me to show
how? :-)

I have some doubt about the story above. Were they playing games by
Japanese rules? I thought Japanese rules were not established for long.

bn 
2k
From: Bruce_Harper@mindlink.bc.ca (Bruce Harper)
Newsgroups: rec.games.chess
Subject: F-S II - Important reminder!
Date: 1 Oct 92 13:49:25 GMT
Organization: MIND LINK! - British Columbia, Canada
Distribution: world

During the first half of the match, it was generally agreed to use the
following three categories for postings:

F-S II Game # (moves)
F-S II Game # (analysis)
F-S II Game # (gossip)

The first category should be reserved for David Fry and others who do us all
the great service of actually posting the moves to each game.  This lets
people skip such postings when they already have the moves once (there's
nothing wrong with having the moves posted several times, but no one wants to
read them several times).

The second category is for analysis of games which have already been posted.
Several people posted opening analysis of Game 12 under the heading "moves".

The third category is for press conferences, non-chess aspects of the match
and (unfortunately) for those who wish to go on and on about Fischer's
personality.  But at least the reader knows what he might be in for when he
reads category three.

To reinforce the point, I would ask people to post their agreement or
disagreement with this system for handling the material relating to the match
(or any other events which take place in the future).  I know David Fry uses
it and I am most grateful.
From: tennis@ziff.com
Newsgroups: rec.games.chess
Subject: Re: Living World Champions
Date: 27 Sep 92 00:41:16 EDT
Organization: Ziff-Davis, Medford MA

In article <1992Sep23.135259.10104@uoft02.utoledo.edu>, dweddin@uoft02.utoledo.edu writes:
> In article <1992Sep23.161847.28348@osf.org>, ron@osf.org (Ron Birnbaum) writes:
>> ---------
>> 
>> Somebody asked for a list of the people, now living, who have held the world
>> Chess Championship title. I haven't seen a response, so - here they are:
>> 
>> Smyslov
>> Botvinnik
>> Spassky
>> Fischer
>> Karpov
>> Kasparov
>> 
>> -Ron
> 
> is MAX EUWE still alive...i thought he was.
> 
> don wedding
> 
I thought Botvinnik had shuffled his mortal coils some time ago...
And of couse, Tal too. :(

Tony Ennis

Newsgroups: rec.games.chess
From: jmh@athena.mit.edu (J Michael Hammond)
Subject: Re: mirror, mirror on the board...
Organization: Massachusetts Institute of Technology
Date: Mon, 28 Sep 1992 11:22:25 GMT

In article <1992Sep28.050207.19253@pony.Ingres.COM> jrb@Ingres.COM (John Black) writes:
>What would you recommend against someone who decided to copy your moves, but
>wouldn't copy them if you made a move which required them to hang a piece (as
>the above does) or get mated in one move?  I realize this isn't a very precise
>definition, but you know what I mean... what would you have recommended to me
>when I was 12 years old and my friends were copying my moves?  Winning combos
>have to be at least a couple moves deep or they'll be detected...

A good line would still be 1. e4 e5  2. Nf3 Nf6  3. Nxe5 Nxe4  4. Qe2.

(When I was 12 years old and my friends were copying my moves, I would
resort to this.)

I forget which semi-legitimate opening book (maybe it was "Practical
Chess Openings?") described 3. ... Nxe4 as "losing at least a Pawn".
If your "first-order non-piece-hanging move-copier" (a purely
theoretical construct whose play, by the way, results in a
deterministic finite zero-sum game of perfect information -- ouch,
stop hitting me) realizes that 4. ...  Qe7 would lose the e4 knight,
he may move 4. ... Nc5 or 4. ... Nf6, at which point you move 5. Nc6,
winning.  If he tries 4.  ... d5 or 4. ...  f5, you have easy tactical
shots which should eventually break your opponent of his habit.

So what does one do after one's first-order non-piece-hanging
move-copying opponent learns not to fall for 3. ... Nxe4 and instead
starts playing 3. ... d6?

Play COCHRANE'S GAMBIT (4. Nxf7) of course!  Live on the edge
against your less-experienced opponents!  Give them a temporary
material gain onto which they can greedily hold!  Beat them into
submission!  Then teach them some of those *really* crazed lines of
the King's Gambit so that you can start sacrificing some SERIOUS
material!!!(repeat ! ad nauseum with raucous evil laughter.)

------------------------------------------------------------------
J. Michael Hammond           The MathWorks, Inc.  | Testers do it
Manager of Software Quality  (voice) 508 653-1415 | over and over!
jmike@mathworks.com          (FAX) 508 653-2997   |
------------------------------------------------------------------
From: beaudoin@ireq-robot.hydro.qc.ca (Martin Beaudoin)
Newsgroups: rec.games.chess
Subject: xics and ICS style 8
Date: 5 Oct 92 01:54:48 GMT
Organization: Le laboratoire de robotique de l'Institut de recherche
	d'Hydro-Quebec

After loosing some nice games by having my telnet link slowing down
dramatically, I've decided to add the ICS style 8 parsing capabilities
to xics in order to cut down on the bandwith needed to send the moves. 

It's working nicely now, as long as the ICS managers will not change the
format too much. My version of xics can now parse style 1 and 8
automagically; it is transparent to the user. I have also added a text
line showing the name of the two opponents (handy if you can't
remember the name of your opponent after a couple of moves...)

I would like to get in contact with someone managing ICS in order to
put the patches somewhere on valkyries.

Thanks!

--
Martin Beaudoin                         mbeaudoin@ireq-robot.hydro.qc.ca
Institut de recherche d'Hydro-Quebec    mbeaudoin@ireq-robot.uucp
Varennes, QC, Canada   J3X 1S1          +1 514 652-8136
Newsgroups: rec.games.chess
From: I0060301@dbstu1.rz.tu-bs.de (Klaus Blumberg)
Subject: F-SII game 14
Organization: Technical University Braunschweig, Germany
Date: Mon, 5 Oct 1992 10:54:25 GMT

for some reason or other i can't discover in the news the moves of game 14.
have just i missed them or is something gone wrong?
can someone pls send them to me? thanx.
Newsgroups: rec.games.chess
From: kbs4580@rigel.tamu.edu (SCHAUB, KEITH BRADLEY)
Newsgroups: rec.games.chess
Subject: Re: Please stop
Date: 1 Oct 92 15:18:00 GMT
Article-I.D.: rigel.1OCT199210185642
Organization: Texas A&M University, Academic Computing Services
News-Software: VAX/VMS VNEWS 1.41

In article <1aduebINNiff@cascade.cs.ubc.ca>, kvdoel@cs.ubc.ca (Kees van den Doel) writes...
>In article <1992Sep30.233850.25643@midway.uchicago.edu> hau4@midway.uchicago.edu writes:
>>...
>>It is not possible, even in principle, to travel at the speed of light.
>>It is possible, however, to solve chess, at least in principle.
>>...
>>	Sven
> 
>That is a *very* bad analogy. It is *logically* impossible that
>chess is not solvable but the impossibility of traveling at
>the speed of light (for a massive object) is a consequence of
>Lorentz's special theory of relativity, which is only an
>hypothesis. In fact in Hilberts general theory of relativity
>superluminal transport is possible.
> 
>--Kees

	Thankyou Kees, at least some people know what there talking about.
Sven aren't you a physics grad. student--you should have known that.
--Keith
Newsgroups: rec.games.chess
From: sloan@cis.uab.edu (Kenneth Sloan)
Subject: Re: What is this notation? Smythescript?
Keywords: Smythescript
Organization: CIS, University of Alabama at Birmingham
Date: Fri, 2 Oct 1992 03:31:58 GMT

In article <1992Oct1.225450.16006@husc3.harvard.edu> elkies@ramanujan.harvard.edu (Noam Elkies) writes:
>...
>for a really compact and opaque notation, list the legal moves from a given
>position in your favorite lexicographical order, so any move may be specified
>by a single character indicating its place in the lexicographic list and
>a 40-move game may be listed in one 80-character line.

Not good enough.  List all legal *games* in your favorite order
and specify the game by it's position in this list.

[Of course, Game 0 should be reserved for the unique game representing
perfect play by both sides - is this game known?]
-- 
Kenneth Sloan                   Computer and Information Sciences
sloan@cis.uab.edu               University of Alabama at Birmingham
(205) 934-2213                  115A Campbell Hall, UAB Station 
(205) 934-5473 FAX              Birmingham, AL 35294-1170
Newsgroups: rec.games.chess
From: alper@sushi.psych.nwu.edu (Theodore M. Alper)
Subject: Re: Wait -- is THIS the sort of thing that the solvability opponents
Organization: Northwestern University, Evanston IL
Date: Sat, 26 Sep 1992 19:02:25 GMT

>BTW, the usual practice of payoff(win, loss, draw) = (1, 0, .5)
>can also be adjusted in various ways, with interesting results.
>Note that Article 17 of the FIDE rules assigns these payoffs (i.e,
>win=1, loss=0, draw=.5).  It is an understandable oversight on the
>part of FIDE (and the other Federations) that they have failed to
>assign payoffs to the cases of "infinite games".

Well, they'll never have to payoff an infinite game, since the players
will never be able to complete it.

In any case, in the context of chess-as-it's-currently-defined, 
one still has practical-solvability (if in an impractical way):
One has an effective way to determine if White can force mate,
Black can force mate, or neither player can force mate. If neither
player can force mate, then either player COULD force a draw, if he
or she wanted to. 
Newsgroups: rec.games.chess
From: mzabel@magnus.acs.ohio-state.edu (Mark A Zabel)
Subject: Re: ( was Re: Please stop )
Organization: The Ohio State University
Date: Thu, 1 Oct 1992 15:14:01 GMT

[Names are deleted to protect the innocent]

>>   Enough already again from a different person. We are tired of
>>having to read your solvability crap.
>
>You don't HAVE TO read it, and before you call it crap look at what you are
>producing.
>

     And if you thought arguing about whether chess is solvable
wasn't boring enough...now we are going to argue about whether we
should argue about whether chess is solvable!!!!!!

AAAARGH!!!  Can anybody's ego allow them to give this whole thing a
rest?  I offer this *sincere* comment as bait to stop.

Gee!  You're all so very very smart.  Gosh!  We're all very
impressed over here, I can tell you!!!

obligatory chess_comment:  Was game 12 bad for Fischer or what?  He
                           didn't seem to get any play the whole
                           game.  I just looked at it briefly, but
                           it looked like a5 was a lemon (among others).

-Mark
Newsgroups: rec.games.chess
From: jpgraham@magnus.acs.ohio-state.edu (John P Graham)
Subject: Chessmaster 3000 features??
Organization: The Ohio State University
Distribution: usa
Date: Tue, 29 Sep 1992 19:31:15 GMT

Can anyone tell me how CM3000 is supposed to estimate 
ratings for its opponent? Is this based on a series of 
stored positions (as in chessplayer 2150) or based on 
actual games played against the program.. if based on 
games .. just one game or a series of games?
Similar questions concerning Grandmaster chess...
Also how effective are the 'different personalities'
claimed by the CM3000 people??
Many thanks in advance .... 
John.
From: Bruce_Harper@mindlink.bc.ca (Bruce Harper)
Newsgroups: rec.games.chess
Subject: Re: F-S Match, ratio wins/draws. WHY?
Date: 1 Oct 92 15:24:47 GMT
Organization: MIND LINK! - British Columbia, Canada
Distribution: world

A good question.  I think there are two possible answers:

1. The format of ten wins being required (draws not counting) means that
treading water by playing for draws is unlikely to produce results.

2. The match is not being played at a particularly high level, so blunders
are occurring on both sides.

Amplifying point 2, Spassky's health might have cost him a few games (I bet
he's feeling better now!), while Fischer's rust might have done the same for
him.

It's possible to add:

3. If you get over $1.5 m if you lose, it makes it a bit easier to take
chances.

All in all, I think 2 is the answer, but 1 plays a part too - I doubt if
either player wants to risk wearing down the other.  Age plays a part in
this.