TESTS FAIL. Checked in the new implementation that only checks the last generation of each branch. Two small cells not found in the test, but logic seems mostly sound so checking in.
TESTS FAIL. Checked in the new implementation that only checks the last generation of each branch. Two small cells not found in the test, but logic seems mostly sound so checking in.

jkomoros/sudoku,jkomoros/sudoku,jkomoros/sudoku