Congratulations on making such a powerful program.

I have tested it with 13 puzzles from several sources and find the program fast.  If I can solve a puzzle, it takes me 5 to 10 minutes
 to do what the program does in 1 second.  Also, if I make a mistake that prevents me solving that puzzle.  Your program is self-correcting, I wish I could be.

Here is a good one for you

800000000
003600000
070090200
050007000
000045700
000100030
001000068
008500010
090000400

The zeros represent blank cells.  I can't fill in one cell using Plan A - slice and dice.  Neither can I fill in one cell by Plan Z -
examining the possibilities for each cell.  If anyone knows how to start this puzzle by just using a logical brain, I would like to hear from you.

The program solves it but takes longer than the usual standard puzzles - what can you expect when you give it a very very hard puzzle.