README

These two specification were received from Stephan Merz on 17 December
2010, along with the following email:

A colleague asked me how I'd write a solution to the N-queens problem
in TLA+.  The result is attached.  The idea is straightforward, and I
assume that you may already have written something similar at some
point, but I'm still sending it to you in case you think it's useful.
(Maybe we could put up some such examples on the TLA+ web site and/or
encourage people to contribute their models, though that would require
some validation?)  TLC can execute the algorithm in no time for 4
queens, but I killed it after an hour for N=5 -- however, it could
still evaluate the definition of Solutions for N=5 in no time.