[Retros] Natch v3.1

[Otto Janko]

Ob behalf of Pascal Wassong who currently cannot post to the retro mailing
list because of a technical problem:

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Hello all,

Ivan Denkovski has found a bug in Natch v3.0.  It didn't find the
solution in some rare cases.  An example is the short game 1.b4 c5 2.b5
Nc6 3.bxc6 b5 4.c7 Bb7 5.c8=B Be4.  More details are in the README file.

This has now been corrected, and the version 3.1 is available at the
usual place.

Pascal
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