[r-t] Bobs only Erin Triples (was: Composition search)

Matthew Frye matthew at frye.org.uk
Fri Dec 4 20:02:02 UTC 2015

> On 4 Dec 2015, at 19:07, Ian Broster <ian at broster.co.uk> wrote:
> > There are 26, excluding rotations.
> I think that there are 140. I made a list once, but lost it long ago. Luckily the internet archive to the rescue!
> https://web.archive.org/web/20050426201814/http://www-users.cs.york.ac.uk/~ianb/solid/plainbobminorbobs.text <https://web.archive.org/web/20050426201814/http://www-users.cs.york.ac.uk/~ianb/solid/plainbobminorbobs.text> 

OK, taking that list as definitive, a little dab of python finds three unique 360’s:
Final list:  ['bbpbbpbpbppbbpbppbbppbbpbbpppp', 'bbpbppbbppbpbppppbbpppbpbbpppp', 'bbpppbppppbbpppbppppbbpppbpppp’]

The one I didn’t give previously can be thought of as WHW with an extra Q-set, giving, eg. WFWHWWOHWIHW, where 7 leads (and HW) have been removed from the first part and inserted in the third part by the F/O/I Q-set. I *think* I knew about this, but forgot it because it’s not a very nice compared to the other two, imho.

Point is, I have no idea how extensive a tree-search is needed for this problem, but such a strategy is probably beyond pencil and paper in reasonable time? Whereas I was able to do it as a teenager in a couple of hours with some basic Q-set considerations.

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