naive encoding yields:
--automatic gen of tile names and correct gen wrt to the blank
(appropriate encoding of inference rules!!!)

--no generalization over operator names.

--conjunctions equivalent to "lower left corner".

--could optimize search by halving state length and writing the
operators only in terms of right-of and top-of.

***after s1.lisp prodigy/ebl is able to place the blank anywhere!
(this is actually trivial. Once it learns not to repeat itself right
away it just randomly traverses the 3x3 board until it reaches the
initial state.