Cunning way to ensure unique solutions in generated Rectangles

puzzles. I generate the grid of rectangles as normal, but before I
place the numbers I run it through a non-deterministic solver
algorithm which tries to do as much as it can with as little
information about where the numbers are going to be. The solver
itself narrows down the number placement when it runs out of steam,
but does so as little as possible. Once it reaches a state where it
has ensured solubility, and then the generation algorithm chooses
random number placement from whatever's left.

Occasionally it paints itself into a corner and can't ensure a
unique solution no matter what happens; in that situation we just
have to give up, generate a fresh grid, and try again.

[originally from svn r5809]

puzzles.but

@@ -578,13 +578,13 @@ numbered square, and (b) the area of each rectangle is equal to the
 number written in its numbered square.
 
 Credit for this game goes to the Japanese puzzle magazine \i{Nikoli}
-\k{nikoli-rect}; I've also seen a Palm implementation at \i{Puzzle Palace}
-\k{puzzle-palace-rect}. Unlike Puzzle Palace's implementation, my version
-automatically generates random grids of any size you like. The quality
-of puzzle design is therefore not quite as good as hand-crafted
-puzzles would be (in particular, a unique solution cannot be
-guaranteed), but on the plus side you get an inexhaustible supply of
-puzzles tailored to your own specification.
+\k{nikoli-rect}; I've also seen a Palm implementation at \i{Puzzle
+Palace} \k{puzzle-palace-rect}. Unlike Puzzle Palace's
+implementation, my version automatically generates random grids of
+any size you like. The quality of puzzle design is therefore not
+quite as good as hand-crafted puzzles would be, but on the plus side
+you get an inexhaustible supply of puzzles tailored to your own
+specification.
 
 \B{nikoli-rect} \W{http://www.nikoli.co.jp/puzzles/7/index_text-e.htm}\cw{http://www.nikoli.co.jp/puzzles/7/index_text-e.htm}