[Retros] Retractor 2.0

Theodore Hwa hwatheod at cs.stanford.edu
Fri Apr 16 22:07:58 EDT 2021

On Fri, 16 Apr 2021, andrew buchanan wrote:

> Hi Theodore & others.
> There's a bunch of last-single-moves proof games from the 2009 Messigny composing tourney:
> https://pdb.dieschwalbe.de/search.jsp?expression=K%3D%27RIFACE%3A2009%27
> Composers focused on maximizing the number of "last single moves" determinable and were all Type C or (if Type A)
> had non-standard or obtrusive material.

Maybe this is a good place to mention that Type C is generally much easier 
for Retractor to solve than the other types (probably expected). When 
tested against the problems at 
https://www.janko.at/Retros/Records/LastMove/index.htm, these are the 
number of problems solved by Retractor:

Type A: 21/59
Type B: 30/59
Type C: 51/60
Type D: 69/161

These numbers will be kept up-to-date at:

Fine print: Type A is considered solved only if Retractor finds 0 
solutions for one side, and 1 solution for the other side. A few of the 
type A problems can be "solved" if Retractor is told which side is to 
move (treating it as a type B problem), but those aren't counted above.

> I have a few suggestions for Retractor v2.0001:
> (1) The default max number of solutions should be infinite or big. 10 is way too small. Because of retro tries, I
> never saw the actual solution for the Type A problem above!
> (2) If you do truncate, you should put a warning on the output, to avert unwarranted joy.
> (3) I would like to be able to try both WTM & BTM (i.e. Type A) without going back to the edit mode.
> (4) Tiniest of possible nits: for me "Retract White next" is disturbing. I personally would prefer "Retract White
> last".

(1) and (2) are in version 2.0.1 (now live); refresh your browser page to 
pick it up.

I'm a little surprised by (1), because I had assumed that mostly people 
would be interested in whether the solution was unique, so I thought 10 
was enough. It has been increased to 100 in version 2.0.1.

Also, version 2.0.1 fixes the problem with the copy buttons. Now the moves 
are displayed in a text box and you can copy it to the clipboard.  Thanks 
to Mario Richter for pointing out this bug.

(3) - it is a little difficult to do with the current design.

(4) - I've left the text as is; I used "next" because White is the 
next player to retract.


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