Moved the creation of a Sudoku from an int[][] from PuzzleCreator (main()) to a factory method in Sudoku, fromIntMatrix()
Fixed the Pair range() function.
Fixed logical errors and cleaned Sudokus. Boolean return types were mixed up, which lead to a big mess.
Fixed semantic errors and logical errors as well as added short-circuits. This SimpleEliminationSolver draft has been tested and does work with a small sample of inputs (possibly more, I just haven't tested those yet)
Added unit tests, which are not comprehensive and sort of thrown together but try to make sure that every solver works right a lot of the time.
Modified fromIntMatrix() to accept cells with zeroes as blanks.
Added the skeleton of a class that will check if a solution exists for a cell with the 'double elimination' strategy that is described (and will eventually be described more thoroughly) in its confirmSolutionExistsFor() javadoc.
Added a new test which is intended not as a unit test, but to explore different new strategies for solution verification using a hard-level unsolved Sudoku puzzle chosen randomly (well, haphazardly) from the internet.