🚀 go-pugleaf

In article <34E9AB23.6EEF@Waisman.Wisc.Edu>, Douglas Swiggum <Swiggum@Waisman.Wisc.Edu> writes:
>I just played a 7 move mate against GNUchess version 4.0.77
>
>(by way of WinBoard 3.6.1)
>
>How is that possible?
>
>Here is the game in PGN format:
>
>[Event "Computer chess game"]
>[Site "DIRAC"]
>[Date "1998.02.16"]
>[Round "-"]
>[White "DMS"]
>[Black "GNU Chess"]
>[Result "1-0"]
>[TimeControl "40/300"]
>
>1. e4 e5 2. Nf3 d6 3. Nc3 Bg4 4. Bc4 h6 5. Nxe5 Bxd1 6. Bxf7+ Ke7 7. Nd5#
>{White mates} 1-0

That's a good one.  The answer is that this line is in GNU Chess's
book!  Actually you transposed out of book and back in, but that
doesn't matter.  The actual line in the book is "e4 e5 Nf3 d6 Bc4 Bg4
Nc3 h6 Ne5 Bd1 Bf7 Ke7 Nd5"

My guess is that this line got there because it's a standard trap
(called Legal's Mate) that is documented in one of the opening books
that was used to prepare the GNU book, probably MCO.  

Most likely in an earlier version of the book, there was a ? after the
key losing move for Black, but it got lost somewhere along the line.
At one time in the history of the GNU book, someone had carefully
included key traps in the book with ?'s to keep GNU from falling into
them and to let GNU know what to do if its opponent fell into one.
Later, as I recall, someone (I forget just who) deleted all the ?
marks but left the bad lines in there, out of some kind of
inexplicable confusion over why the ?  marks had to be there.  I
thought I had complained loudly enough to get this fixed many versions
ago, but evidently not.  The current book has *no* ?'s, but obviously
still has some lines that are absolutely losing for one player or the
other.

-- 
Tim Mann <mann@pa.dec.com>
http://www.research.digital.com/SRC/personal/Tim_Mann/