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Natch is a software solving a special kind of chess problems : proof games. It works on any Unix system (like GNU/Linux) and also on the Windows system in DOS mode.

iNatch is graphical interface for proof games which lets you use Natch. iNatch has it's own page.

Better than a lot of words, an example is a good way to show what Natch is able to do :

1st commendation, feenschach 1982
15+12. Position after the 23rd move
of White. How did the game go ?

The solution is :

1.e4 d5 2.e5 Kd7 3.e6+ Kc6 4.exf7 e5 5.h4 e4 6.h5 e3 7.Rh4 e2 8.Ra4 exf1=B 9.Qg4 Bc4 10.d3 d4 11.dxBc4 d3 12.Sf3 d2+ 13.Ke2 d1=R 14.Se1 Rd6 15.Bd2 Rg6 16.hxRg6 h5 17.Bb4 h4 18.Sc3 h3 19.Rd1 h2 20.Rd7 h1=S 21.Sd1 Sg3+ 22.fxSg3 Se7 23.Qe6#

This problem shows the Frolkin theme with a Rook, a Bishop and a Knight.

Natch solves this problem in few seconds :

These results do not mean that Natch is able to verify every problem. There are many kinds of positions where Natch needs days, if not weeks, to find a solution. But hopefully it may help SPG composers.


The current stable version is 2.4 (december 2005).

The program is distributed under the GNU GPL license (see the file COPYING). The main form of distribution is the source files that will compile without problems on most Unix systems : Natch-2.4.tar.gz (192 Kb).

Most users having a Windows system will probably prefer the ready to use distribution (as a DOS program) : (115 Kb).

Natch on Vista

I received reports that on Vista, Natch stops with the error "Unable to allocate memory for hash table." when using the option --hash-size (-t) with a value larger than 27. This problem is due to the fact that Windows Vista restricts non-Win32 apps to 32 MB of memory.

I have recompiled Natch with another compiler which removes this limit. Download if you have this problem.

Beta version

Version 2.4 has a bug (and all previous ones). It doesn't find the solution in the following position : rs1q1bsr/1ppkpppp/4p3/1K1b4/p7/8/PPPP1PPP/RSBQ1BSR (position after 7.0 moves). This Beta version corrects this bug. Version 2.5 will be a bug correction release only. No new features will be added. Please report any bugs in this version : Natch-2.5Beta.tar.gz.

Here is the corresponding precompiled Windows version (a DOS program in fact). It should work on Vista :

If you have questions or comments, send a mail to .

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