[Retros] Retractor 2.3 released with promotion pawn capture counting

[Theodore Hwa]

Retractor 2.3 has been released! Now Retractor can count pawn captures 
coming from promoted pieces that are on the board. Here is an example of a 
problem that Retractor 2.3 can solve which couldn't be solved by previous 
versions:

Roberto Osorio & Jorge Lois
8/5p1p/8/8/8/P3P1P1/rPPPRP1P/Qqk1KR1r
Duplex. Last move?

For the case where White made the last move, Retractor 2.3 can now 
eliminate the incorrect last move Rg1xQf1 because it would take too many 
pawn captures to produce 3 promoted Black pieces.

Here's a longer problem that Retractor 2.3 can't quite solve, but it can 
reduce the number of possibilities to just
11 solutions, all but one of which can then be eliminated by a human.

A. Kornilov & A. Frolkin
Phénix 189-190, Dec. 2009
2QNkRnn/PpRpp1rq/1Kp2prB/6p1/4P3/7P/1P1pPP1P/8
Last 10 single moves?

For this problem, you need to set the solver with parameters: Solve depth 
10, Extra depth 5, Max solutions 20. It will take some time to produce the 
11 possibilities.

The latest version can be found in the usual place: 
https://xenon.stanford.edu/~hwatheod/retractor2/retractor.html

You may need to do a hard-refresh (shift+refresh) in your browser to 
obtain the latest version. Make sure it says Retractor 2.3.

Ted Hwa