Stream-based sudoku solver

A friend of mine was talking about a sudoku solver he'd written in python as an programming challenge, and confessed that Peter Norvig's version was more elegant, in part because he used generators. Python generators are infinite streams -- so this sounded like something I could tackle with Aqueduct.

I though a bit about how to solve Sudoku using streams (I didn't want to cheat and actually read PN's solution before trying it myself). Basically, I reasoned that I could use streams to brute force a solution in the same way I did for the N-queens solver. Each one of the 9 x 9 cells in the sudoko board would be its own pipeline stage. It would combine a stream of all valid input boards with all possible values of that cell, filter out invalid moves, and pass new boards on to the next cell.