diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..d646835
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+*.pyc
+__pycache__/
diff --git a/puzzles.py b/puzzles.py
old mode 100755
new mode 100644
index 1d7dc00..62f5199
--- a/puzzles.py
+++ b/puzzles.py
@@ -1,67 +1,58 @@
-#!env python3
+#!/usr/bin/env python3
 # Eryn Wells <eryn@erynwells.me>
+
 '''
 Parser for puzzles in the ./puzzles directory.
 '''
 
-import argparse
-import os.path
-import sys
+import sudoku
 
-from sudoku import Sudoku, solvers
 
 euler = []
 norvig = []
 
-def parse_puzzle_library(path, quiet=True):
-    if not quiet:
-        print('Parsing puzzles in {}'.format(path))
-    puzzles = _get_puzzles(path, quiet)
-    return puzzles
 
-def _get_puzzles(filename, quiet):
+def parse_euler(filename='./puzzles/euler.txt'):
     with open(filename, 'r') as f:
-        puzzles = f.readlines()
-    return (_parse_puzzle(p, quiet) for p in puzzles if p)
+        puzzle_lines = f.readlines()
 
-def _parse_puzzle(puzzle, quiet):
-    puzzle = puzzle.strip()
-    if len(puzzle) == 81:
-        if not quiet:
-            print("Parsing  '{}'".format(puzzle))
-        board = (int('0' if x == '.' else x) for x in puzzle)
-        return Sudoku(board=board)
-    else:
-        if not quiet:
-            print("Skipping '{}'".format(puzzle))
-        return None
+    for puzzle in puzzle_lines:
+        # Chop the newline
+        if puzzle[-1] == '\n':
+            puzzle = puzzle[:-1]
+        print('Parsing puzzle: {}'.format(puzzle))
+        if len(puzzle) != 81:
+            continue
+        kwargs = {}
+        for idx in range(len(puzzle)):
+            sq = puzzle[idx]
+            if sq not in '1234567890.':
+                continue
+            sq_int = 0 if sq == '.' else int(sq)
+            x, y = int(idx % 9), int(idx / 9)
+            if sq_int != 0:
+                kwargs[sudoku.Board.xy_kwargs_key(x, y)] = sq_int
+        euler.append(sudoku.Board(**kwargs))
 
-def parse_args(args):
-    parser = argparse.ArgumentParser()
-    parser.add_argument('--solver', '-s', default=None,
-                        help='The solver to use to solve this puzzle.')
-    parser.add_argument('--verbose', '-v', action='store_true', default=False,
-                        help='Print extra information when parsing puzzle libraries.')
-    parser.add_argument('library',
-                        help='A library file containing puzzles, one per line.')
-    parser.add_argument('indexes', metavar='N', nargs='+', type=int,
-                        help='0-based indexes of puzzles in the library')
-    return parser.parse_args(args)
 
-def main():
-    args = parse_args(sys.argv[1:])
-    puzzle_library = list(parse_puzzle_library(args.library, quiet=not args.verbose))
-    for i in args.indexes:
-        puzzle = puzzle_library[i]
-        print(puzzle)
-        if args.solver is not None:
-            try:
-                solver = getattr(solvers, args.solver)
-                puzzle.solve(solver.solve)
-            except AttributeError:
-                print('No solver named {}'.format(args.solver))
-            print(puzzle)
-    return 0
+def parse_norvig(filename='./puzzles/norvig.txt'):
+    with open(filename, 'r') as f:
+        puzzle_lines = f.readlines()
 
-if __name__ == '__main__':
-    sys.exit(main())
+    for puzzle in puzzle_lines:
+        # Chop the newline
+        if puzzle[-1] == '\n':
+            puzzle = puzzle[:-1]
+        print('Parsing puzzle: {}'.format(puzzle))
+        if len(puzzle) != 81:
+            continue
+        kwargs = {}
+        for idx in range(len(puzzle)):
+            sq = puzzle[idx]
+            if sq not in '1234567890.':
+                continue
+            sq_int = 0 if sq == '.' else int(sq)
+            x, y = int(idx % 9), int(idx / 9)
+            if sq_int != 0:
+                kwargs[sudoku.Board.xy_kwargs_key(x, y)] = sq_int
+        norvig.append(sudoku.Board(**kwargs))
diff --git a/puzzles/norvig.txt b/puzzles/norvig.txt
index a68d542..c8429cc 100644
--- a/puzzles/norvig.txt
+++ b/puzzles/norvig.txt
@@ -93,3 +93,4 @@
 .5..9....1.....6.....3.8.....8.4...9514.......3....2..........4.8...6..77..15..6.
 .....2.......7...17..3...9.8..7......2.89.6...13..6....9..5.824.....891..........
 3...8.......7....51..............36...2..4....7...........6.13..452...........8..
+
\ No newline at end of file
diff --git a/sudoku.py b/sudoku.py
new file mode 100644
index 0000000..964e6be
--- /dev/null
+++ b/sudoku.py
@@ -0,0 +1,237 @@
+#!/usr/bin/env python3
+# Eryn Wells <eryn@erynwells.me>
+
+'''
+A Sudoku solver.
+'''
+
+import copy
+import logging
+import math
+
+LOG = logging.getLogger(__name__)
+
+
+class Board(dict):
+    def __init__(self, size=9, **kwargs):
+        self.size = size
+
+        # Verify size is a perfect square. The sqrt(size) is also the dimension of each box on the
+        # Sudoku grid.
+        self.box_size = int(math.sqrt(size))
+        assert self.box_size == int(self.box_size), 'Invalid size; value must be a perfect square'
+
+        # The range of possible values for a square.
+        self.possible_values = range(1, self.size + 1)
+
+        # Make the grid.
+        super(Board, self).__init__([(Board.xy_key(x, y), list(self.possible_values))
+                                     for x in range(self.size)
+                                     for y in range(self.size)])
+        for square in self:
+            initial_value = kwargs.get(Board.xy_kwargs_key(*square))
+            if initial_value is None:
+                continue
+            if initial_value not in self.possible_values:
+                raise ValueError('Invalid initial value for square ({}, {}): {}'.format(x, y, initial_value))
+            LOG.debug('Setting initial value of {} to {}'.format(square, initial_value))
+            self.assign(square, [initial_value])
+
+    @classmethod
+    def xy_key(self, x, y):
+        '''Given {x} and {y}, generate a key to refer to the square at coordinate (x, y) in the grid.'''
+        return (int(x), int(y))
+
+    @classmethod
+    def xy_kwargs_key(self, x, y):
+        '''
+        Given {x} and {y}, generate a key to refer to the square in the __init__ kwargs at coordinate (x, y) in the
+        grid.
+        '''
+        return 'x{}y{}'.format(x, y)
+
+    @property
+    def solved(self):
+        '''
+        Determines if the board has been solved. First, determine if all squares have no more than one value (i.e. they
+        have had values assigned to them). If not, return False. If so, check each unit (rows, columns, and boxes) to
+        make sure that each has one and only one of each value in the range of possible values for a unit. If not,
+        return False; otherwise, return True.
+        '''
+        if not all(len(s) == 1 for s in self.values()):
+            return False
+
+        def validate_unit(unit):
+            '''
+            Validate {unit} by ensuring it has exactly 1 of each value in the range of possible values.
+            '''
+            necessary_values = list(self.possible_values)
+            for square, values in unit.items():
+                v = values[0]
+                if v in necessary_values:
+                    necessary_values.remove(v)
+                else:
+                    return False
+            if len(necessary_values) != 0:
+                return False
+            return True
+
+        return (    all(validate_unit(self.row(r)) for r in range(self.size))
+                and all(validate_unit(self.col(c)) for c in range(self.size))
+                and all(validate_unit(self.box(x, y))
+                        for x in range(0, self.size, self.box_size)
+                        for y in range(0, self.size, self.box_size)))
+
+    def row(self, idx):
+        '''
+        Return a dict of all squares in the {idx}'th row.
+        '''
+        assert idx >= 0 and idx < self.size, 'Invalid row index; value must be >= 0 and < {}'.format(self.size)
+        # key[1] is Y coordinate in the grid.
+        return {k: v for k, v in self.items() if k[1] == idx}
+
+    def col(self, idx):
+        '''
+        Return a dict of all squares in the {idx}'th column.
+        '''
+        assert idx >= 0 and idx < self.size, 'Invalid column index; value must be >= 0 and < {}'.format(self.size)
+        # key[0] is X coordinate in the grid.
+        return {k: v for k, v in self.items() if k[0] == idx}
+
+    def box(self, x, y):
+        '''
+        Given a square at coordinates ({x}, {y}), return a dictionary containing the squares that make up the box that
+        contains the point.
+        '''
+        bx = int(x / self.box_size) * self.box_size
+        by = int(y / self.box_size) * self.box_size
+        bx_range = range(bx, bx + self.box_size)
+        by_range = range(by, by + self.box_size)
+        return {k: v for k, v in self.items() if k[0] in bx_range and k[1] in by_range}
+
+    def peers(self, x, y):
+        '''
+        Generate and return a list of peers for the square at coordinates ({x}, {y}). Peers are defined as all the
+        squares in the same row, column, and box as the given square.
+        '''
+        # Generate a dictionary of all the squares in the row, column, and box containing the given square.
+        peers = dict(list(self.row(y).items()) + list(self.col(x).items()) + list(self.box(x, y).items()))
+        # Remove the given square.
+        del peers[Board.xy_key(x, y)]
+        return peers
+
+    def clear(self, squares=None):
+        '''
+        Clear the board. Resets each square's possible value list to the full range of possible values for this board.
+        '''
+        for square in (self if squares is None else squares):
+            self.assign(square, list(self.possible_values))
+
+    def solve(self):
+        return self.search()
+
+    def search(self):
+        '''
+        Search for a solution, depth-first. Return the solved Board as a new instance of this class.
+        '''
+        if self.solved:
+            return self
+
+        # Chose the square with the fewest possible values.
+        _, smallest = min((len(self[sq]), sq) for sq in self if len(self[sq]) > 1)
+        # Deepcopy the board.
+        trials = []
+        for v in self[smallest]:
+            trial_board = copy.deepcopy(self)
+            if trial_board.assign(smallest, [v]):
+                trials.append(trial_board)
+                trial_board.search()
+            else:
+                trials.append(None)
+        for t in trials:
+            if t is not None:
+                return t
+        return False
+
+
+    def assign(self, square, value):
+        '''
+        Assign {value} to {square}. {value} is expected to be an iterable (a list). {key} should be a valid (x, y)
+        coordinate pair for referencing a square on the board.
+        '''
+        LOG.debug('Assigning values {} to square {}.'.format(value, square))
+        removed_values = set(self[square]) - set(value)
+        for v in removed_values:
+            if not self.eliminate(square, v):
+                return False
+        return True
+
+    def eliminate(self, square, value):
+        '''
+        Eliminate {value} from {square}, propagating changes to the squares peers as necessary. This process involves
+        two logical rules of Sudoku. First, if a square is reduced to a single possible value, assign that value to the
+        square and remove the value from the possible value lists of its peers. Second, if a unit has only one square
+        that can hold a value, put the value in that square and propagate that change to its peers.
+        '''
+        if value not in self[square]:
+            LOG.debug('Value {} not in square {}; skipping'.format(value, square))
+            return True
+
+        # Update peer value list.
+        super(Board, self).__setitem__(square, [v for v in self[square] if v != value])
+        LOG.debug('Eliminating {} from square {}'.format(value, square))
+
+        # (1) If a square is reduced to one value, eliminate that value from its peers.
+        if len(self[square]) == 0:
+            # Whoops. Removed the last value... We have a contradiction now.
+            LOG.error('Removed last value from square {}'.format(square))
+            return False
+        elif len(self[square]) == 1:
+            # One value left in this square. Propagate changes to its peers.
+            LOG.debug('One value left in square {}; eliminating {} from its peers'.format(square, self[square][0]))
+            for peer in self.peers(*square):
+                if not self.eliminate(peer, self[square][0]):
+                    return False
+
+        # (2) If a unit has only one square for a value, put it there.
+        for unit in (self.row(square[1]), self.col(square[0]), self.box(*square)):
+            places = [sq for sq in unit if value in unit[sq]]
+            if len(places) == 0:
+                LOG.error('No place for value {} to go in unit {}'.format(value, unit))
+                return False
+            elif len(places) == 1:
+                LOG.debug('One place for value {} to be in unit {}; setting'.format(value, unit))
+                self.assign(places[0], [value])
+
+        return True
+
+    def __delitem__(self, key):
+        # Don't allow deleting keys from self.
+        pass
+
+    def __str__(self):
+        lines = []
+        box_lines = []
+        square_size = len(str(self.size))
+        for y in range(self.size):
+            row_squares = []
+            box_squares = []
+            for x in range(self.size):
+                square = self.get(Board.xy_key(x, y))
+                if len(square) == 1:
+                    box_squares.append(str(square[0]).center(square_size))
+                else:
+                    box_squares.append('.'.center(square_size))
+                if len(box_squares) == self.box_size:
+                    row_squares.append(' '.join(box_squares))
+                    box_squares = []
+            # Print a divider between boxes.
+            box_lines.append(' | '.join(row_squares))
+            if len(box_lines) == self.box_size:
+                lines.append('\n'.join(box_lines))
+                box_lines = []
+                if y < self.size - 1:
+                    # Don't print a divider on the last line.
+                    box_dividers = ['-' * ((square_size + 1) * self.box_size - 1) for box in range(self.box_size)]
+                    lines.append('\n{}\n'.format('-+-'.join(box_dividers)))
+        return ''.join(lines)
diff --git a/sudoku/__init__.py b/sudoku/__init__.py
deleted file mode 100644
index 3cb0572..0000000
--- a/sudoku/__init__.py
+++ /dev/null
@@ -1,230 +0,0 @@
-#!env python3
-# Eryn Wells <eryn@erynwells.me>
-'''
-A Sudoku puzzle solver.
-'''
-
-import itertools
-import math
-
-BOLD_SEQUENCE = '\x1B[1m'
-UNBOLD_SEQUENCE = '\x1B[0m'
-
-class Sudoku:
-    def __init__(self, size=3, board=None):
-        self._size = size
-        sz4 = size ** 4
-        if board:
-            self._board = bytearray(board)[:sz4]
-            self._clues = frozenset(i for i in range(len(self._board)) if self._board[i] != 0)
-        else:
-            self._board = bytearray(sz4)
-            self._clues = frozenset()
-        self._possible_values = None
-
-    @property
-    def size(self):
-        '''
-        The size of the board. This dictates the length of one side of the boxes that the board is subdivided into.
-        '''
-        return self._size
-
-    @property
-    def row_size(self):
-        '''
-        The length of a row or column, or the area of a box in the grid.
-        '''
-        return self.size ** 2
-
-    @property
-    def grid_size(self):
-        '''
-        The total number of squares in the grid.
-        '''
-        return self.size ** 4
-
-    @property
-    def all_squares(self):
-        '''
-        Iterator of xy-coordinates for every square in the grid.
-        '''
-        return itertools.product(range(self.row_size), repeat=2)
-
-    @property
-    def all_boxes(self):
-        '''
-        Iterator of xy-coordinates for every box in the grid.
-        '''
-        return itertools.product(range(self.size), repeat=2)
-
-    @property
-    def possible_values(self):
-        '''
-        The set of valid values for any grid square. This method does not account for values made invalid by already
-        being present in a peer of a given square.
-        '''
-        if not self._possible_values:
-            self._possible_values = set(range(1, self.row_size + 1))
-        return self._possible_values
-
-    def possible_values_for_square(self, x, y):
-        value = self.get(x, y)
-        if value:
-            return {value}
-        else:
-            peers = self.peers(x, y)
-            return self.possible_values - peers
-
-    @property
-    def rows(self):
-        return self._apply_index_ranges(self.index_rows)
-
-    @property
-    def columns(self):
-        return self._apply_index_ranges(self.index_columns)
-
-    @property
-    def boxes(self):
-        return self._apply_index_ranges(self.index_boxes)
-
-    def peers(self, x, y):
-        '''
-        Return a set of values of the peers for a given square.
-        '''
-        return {self._board[i] for i in self.index_peers(x, y) if self._board[i] != 0}
-
-    @property
-    def index_rows(self):
-        '''
-        Return an iterable of ranges of indexes into the board, each defining a row.
-        '''
-        return (self._row(i) for i in range(self.row_size))
-
-    @property
-    def index_columns(self):
-        '''
-        Return an iterable of ranges of indexes into the board, each defining a column.
-        '''
-        return (self._column(i) for i in range(self.row_size))
-
-    @property
-    def index_boxes(self):
-        '''
-        Return an iterable of ranges of indexes into the board, each defining a box.
-        '''
-        return (self._box(x, y) for (x,y) in self.all_boxes)
-
-    def index_peers(self, x, y):
-        '''
-        Return a set of the peers, indexes into the board, for a given square.
-        '''
-        idx = self._xy_to_idx(x, y)
-        box = int(x / self.size), int(y / self.size)
-        return (set(self._row(y)) | set(self._column(x)) | set(self._box(*box))) - {idx}
-
-    def _row(self, r):
-        row_size = self.row_size
-        return range(r * row_size, r * row_size + row_size)
-
-    def _column(self, c):
-        return range(c, self.grid_size, self.row_size)
-
-    def _box(self, x, y):
-        size = self.size
-        row_size = self.row_size
-        offx, offy = (x * size, y * size * row_size)
-
-        def _range(i):
-            start = (offy + i * row_size) + offx
-            return range(start, start + size)
-
-        ranges = itertools.chain(*[_range(i) for i in range(size)])
-        return ranges
-
-    @property
-    def solved(self):
-        expected = self.possible_values
-        all_groups = itertools.chain(self.rows, self.columns, self.boxes)
-        return all(expected == set(g) for g in all_groups)
-
-    def solve(self, solver):
-        return solver(self)
-
-    def get(self, x, y):
-        idx = self._xy_to_idx(x, y)
-        value = self._board[idx]
-        return None if value == 0 else value
-
-    def set(self, x, y, value):
-        if value not in self.possible_values:
-            raise ValueError('{} not in set of possible values {}'.format(value, self.possible_values))
-
-        peers = self.peers(x, y)
-        if peers == self.possible_values:
-            raise NoPossibleValues('Peer set for ({},{}) contains all possible values'.format(x, y))
-        if value in peers:
-            raise ValueExistsInPeers('{} already exists in the peer set for ({},{})'.format(value, x, y))
-
-        self._set(x, y, value)
-
-    def unset(self, x, y):
-        self._set(x, y, 0)
-
-    def _set(self, x, y, value):
-        idx = self._xy_to_idx(x, y)
-        if idx in self._clues:
-            raise SquareIsClue('Cannot set clue square ({},{})'.format(x, y))
-        self._board[idx] = value
-
-    def _xy_to_idx(self, x, y):
-        return y * self.row_size + x
-
-    def _apply_index_ranges(self, ranges):
-        return ((self._board[i] for i in r) for r in ranges)
-
-    def __repr__(self):
-        return "{}(size={}, board='{}')".format(self.__class__.__name__,
-                                                self.size,
-                                                ''.join(str(i) for i in self._board))
-
-    def __str__(self):
-        field_width = len(str(max(self.possible_values)))
-        spacer = '{0}{1}{0}'.format('+', '+'.join(['-' * (field_width * self.size) for _ in range(self.size)]))
-
-        fmt = ''
-        for (y,x) in self.all_squares:
-            if x == 0:
-                if y % self.size == 0:
-                    if y != 0:
-                        fmt += '\n'
-                    fmt += '{spacer}'
-                fmt += '\n'
-
-            if x % self.size == 0:
-                fmt += '|'
-
-            idx = self._xy_to_idx(x,y)
-            if idx in self._clues:
-                bold = BOLD_SEQUENCE
-                unbold = UNBOLD_SEQUENCE
-            else:
-                bold = unbold = ''
-            fmt += '{bold}{{board[{i}]:^{{width}}}}{unbold}'.format(i=idx, bold=bold, unbold=unbold)
-
-            if x == (self.row_size - 1):
-                fmt += '|'
-        fmt += '\n{spacer}'
-
-        return fmt.format(board=[str(i) if i != 0 else ' ' for i in self._board], spacer=spacer, width=field_width)
-
-class SudokuError(Exception):
-    pass
-
-class SquareIsClue(SudokuError):
-    pass
-
-class NoPossibleValues(SudokuError):
-    pass
-
-class ValueExistsInPeers(SudokuError):
-    pass
diff --git a/sudoku/solvers/__init__.py b/sudoku/solvers/__init__.py
deleted file mode 100644
index 2f2ffed..0000000
--- a/sudoku/solvers/__init__.py
+++ /dev/null
@@ -1,6 +0,0 @@
-# Eryn Wells <eryn@erynwells.me>
-'''
-A library of Sudoku solvers.
-'''
-
-from . import backtracker, dlx
diff --git a/sudoku/solvers/backtracker.py b/sudoku/solvers/backtracker.py
deleted file mode 100644
index d58fad2..0000000
--- a/sudoku/solvers/backtracker.py
+++ /dev/null
@@ -1,61 +0,0 @@
-# Eryn Wells <eryn@erynwells.me>
-
-from .. import SquareIsClue, ValueExistsInPeers, NoPossibleValues
-
-class Backtrack(Exception):
-    pass
-
-def solve(sudoku):
-    '''
-    Implements a recursive backtracking Sudoku solver.
-    '''
-    return _solve_square(sudoku, 0, 0)
-
-def _solve_square(sudoku, x, y):
-    should_backtrack = False
-    for value in sudoku.possible_values:
-        should_backtrack = False
-        try:
-            sudoku.set(x, y, value)
-        except SquareIsClue:
-            # Do nothing with this square; continue on to the next square below.
-            pass
-        except ValueExistsInPeers:
-            # Try next value.
-            should_backtrack = True
-            continue
-        except NoPossibleValues:
-            # Need to backtrack.
-            should_backtrack = True
-            break
-
-        print('\r{!r}'.format(sudoku), end='', flush=True)
-
-        next_coord = _next_coord(sudoku, x, y)
-        if not next_coord:
-            break
-
-        try:
-            return _solve_square(sudoku, *next_coord)
-        except Backtrack:
-            should_backtrack = True
-            continue
-
-    if should_backtrack:
-        try:
-            sudoku.unset(x, y)
-        except SquareIsClue:
-            pass
-        raise Backtrack()
-
-    print()
-
-    return sudoku
-
-def _next_coord(sudoku, x, y):
-    x += 1
-    if x >= sudoku.row_size:
-        (x, y) = (0, y + 1)
-    if y >= sudoku.row_size:
-        return None
-    return (x, y)
diff --git a/sudoku/solvers/dlx.py b/sudoku/solvers/dlx.py
deleted file mode 100644
index 39e4b98..0000000
--- a/sudoku/solvers/dlx.py
+++ /dev/null
@@ -1,137 +0,0 @@
-# Eryn Wells <eryn@erynwells.me>
-
-from collections import namedtuple
-from enum import Enum
-from .. import SquareIsClue, ValueExistsInPeers, NoPossibleValues
-
-class Backtrack(Exception):
-    pass
-
-class ConstraintKind(Enum):
-    CELL = 1
-    ROW = 2
-    COL = 3
-    BOX = 4
-
-Constraint = namedtuple('CellConstraint', ['kind', 'index', 'value'])
-Possibility= namedtuple('Possibility', ['row', 'col', 'value'])
-
-class Node:
-    '''
-    A doubly-linked list node that is a member of two distinct lists. One list is the row it is a member of. The other
-    list is the column it is a member of.
-    '''
-    def __init__(self):
-        # Horizontal linked list. West is "previous", east is "next".
-        self.west = self.east = self
-        # Vertical linked list. North is "previous", south is "next".
-        self.north = self.south = self
-
-    def insert_after_in_row(self, node):
-        self._insert(node, 'west', 'east')
-
-    def insert_before_in_col(self, node):
-        self._insert(node, 'south', 'north')
-
-    def iterate_row(self):
-        return self._iterate('east')
-
-    def iterate_col(self):
-        return self._iterate('south')
-
-    def _insert(self, node, prev_attr, next_attr):
-        self_east = getattr(self, next_attr)    # Save my old next node
-        setattr(self, next_attr, node)          # My next points to the new node
-        setattr(node, next_attr, self_east)     # New node's next points to the old next
-        setattr(node, prev_attr, self)          # New node's prev points to me
-        if self_east:
-            setattr(self_east, prev_attr, node) # Old next's prev points to the new node
-
-    def _iterate(self, next_attr):
-        cur = self
-        while cur:
-            yield cur
-            cur = getattr(cur, next_attr)
-            if cur == self:
-                break
-
-class Header(Node):
-    '''
-    A column header, including a count of the number of rows in this column.
-    '''
-    def __init__(self, constraint):
-        Node.__init__(self)
-        self.constraint = constraint
-        self.number_of_rows = 0
-
-    def append(self, node):
-        self.insert_before_in_col(node)
-        self.number_of_rows += 1
-        node.header = self
-
-class Cell(Node):
-    '''
-    A cell in the DLX matrix.
-    '''
-    def __init__(self, possibility):
-        super(Cell, self).__init__()
-        self.header = None
-        self.possibility = possibility
-
-    def __repr__(self):
-        return '{}({})'.format(self.__class__.__name__, self.possibility)
-
-def solve(sudoku):
-    '''
-    Implements DLX, Don Knuth's Dancing Links version of Algorithm X, for solving exact cover problems.
-    '''
-    # TODO: Construct the matrix based on the provided sudoku.
-    # TODO: Perform the algorithm on the matrix.
-    # TODO: With the solution from running the algorithm above, fill in the sudoku.
-    return sudoku
-
-def _build_matrix(sudoku):
-    # 1. Create headers for all columns.
-    headers = _build_headers(sudoku)
-    _build_rows(sudoku, headers)
-    return headers
-
-def _build_headers(sudoku):
-    head = None
-    cur = None
-
-    def _insert_header(data):
-        header = Header(data)
-        if cur:
-            cur.insert_after_in_row(header)
-        return header
-
-    # Cell constraints
-    for i in range(sudoku.grid_size):
-        cur = _insert_header(Constraint(ConstraintKind.CELL, i, None))
-
-    # Row, Col, and Box constraints
-    for kind in (ConstraintKind.ROW, ConstraintKind.COL, ConstraintKind.BOX):
-        for i in range(sudoku.row_size):
-            for value in sudoku.possible_values:
-                cur = _insert_header(Constraint(kind, i, value))
-
-    # Head points to the first column header
-    head = cur.east
-
-    return head
-
-def _build_rows(sudoku, headers):
-    for (index, coords) in enumerate(sudoku.all_squares):
-        board_value = sudoku.get(*coords)
-        possibilities = sudoku.possible_values_for_square(*coords)
-        for value in possibilities:
-            cur = None
-            for col in headers.iterate_row():
-                if col.constraint.index != index:
-                    continue
-                cell = Cell(Possibility(*coords, value))
-                col.append(cell)
-                if cur:
-                    cur.insert_after_in_row(cell)
-                cur = cell
diff --git a/sudoku/test.py b/sudoku/test.py
deleted file mode 100644
index b8fccd2..0000000
--- a/sudoku/test.py
+++ /dev/null
@@ -1,89 +0,0 @@
-#!env python3
-# Eryn Wells <eryn@erynwells.me>
-'''
-Unit tests for the Sudoku module.
-'''
-
-import unittest
-import sudoku
-
-class Sudoku4TestCase(unittest.TestCase):
-    def setUp(self):
-        self.board = sudoku.Sudoku(size=2)
-
-class Sudoku4BasicTests(Sudoku4TestCase):
-    def test_that_board_is_sane(self):
-        self.assertEqual(self.board.size, 2)
-        self.assertEqual(len(self.board._board), 2**4)
-
-    def test_rows(self):
-        expected_rows = [
-            [ 0,  1,  2,  3],
-            [ 4,  5,  6,  7],
-            [ 8,  9, 10, 11],
-            [12, 13, 14, 15]
-        ]
-        for (row, exrow) in zip(self.board.index_rows, expected_rows):
-            row_list = list(row)
-            with self.subTest(row=row_list, ex=exrow):
-                self.assertEqual(row_list, exrow)
-
-    def test_columns(self):
-        expected_columns = [
-            [0, 4,  8, 12],
-            [1, 5,  9, 13],
-            [2, 6, 10, 14],
-            [3, 7, 11, 15]
-        ]
-        for (col, excol) in zip(self.board.index_columns, expected_columns):
-            col_list = list(col)
-            with self.subTest(col=col_list, ex=excol):
-                self.assertEqual(col_list, excol)
-
-    def test_boxes(self):
-        expected_boxes = {
-            (0,0): set([ 0,  1,  4,  5]),
-            (1,0): set([ 2,  3,  6,  7]),
-            (0,1): set([ 8,  9, 12, 13]),
-            (1,1): set([10, 11, 14, 15]),
-        }
-        for (coord, exbox) in expected_boxes.items():
-            with self.subTest(sq=coord, ex=exbox):
-                sq = set(self.board._box(*coord))
-                self.assertEqual(sq, exbox)
-
-    def test_peers(self):
-        expected_peers = {
-            (0,0): set([1, 2, 3, 4,  8, 12, 5]),
-            (1,0): set([0, 2, 3, 5,  9, 13, 4]),
-            (2,0): set([0, 1, 3, 6, 10, 14, 7]),
-            (3,0): set([0, 1, 2, 7, 11, 15, 6]),
-
-            (0,1): set([5, 6, 7, 0,  8, 12, 1]),
-            (1,1): set([4, 6, 7, 1,  9, 13, 0]),
-            (2,1): set([4, 5, 7, 2, 10, 14, 3]),
-            (3,1): set([4, 5, 6, 3, 11, 15, 2]),
-
-            (0,2): set([9, 10, 11, 0, 4, 12, 13]),
-            (1,2): set([8, 10, 11, 1, 5, 13, 12]),
-            (2,2): set([8,  9, 11, 2, 6, 14, 15]),
-            (3,2): set([8,  9, 10, 3, 7, 15, 14]),
-
-            (0,3): set([13, 14, 15, 0, 4, 8, 9]),
-            (1,3): set([12, 14, 15, 1, 5, 9, 8]),
-            (2,3): set([12, 13, 15, 2, 6, 10, 11]),
-            (3,3): set([12, 13, 14, 3, 7, 11, 10]),
-        }
-        for (coords, expeers) in expected_peers.items():
-            with self.subTest(coord=coords, ex=expeers):
-                peers = self.board.index_peers(*coords)
-                self.assertEqual(peers, expeers)
-
-class Sudoku4SolvedTests(Sudoku4TestCase):
-    def test_that_an_empty_board_is_not_solved(self):
-        self.assertFalse(self.board.solved)
-
-    def test_simple_solution_is_solved(self):
-        board = (int(i) for i in '1234341221434321')
-        self.board = sudoku.Sudoku(2, board)
-        self.assertTrue(self.board.solved)
diff --git a/tests.py b/tests.py
new file mode 100644
index 0000000..32dabd1
--- /dev/null
+++ b/tests.py
@@ -0,0 +1,128 @@
+#!/usr/bin/env python3
+# Eryn Wells <eryn@erynwells.me>
+
+'''
+Tests for sudoku.
+'''
+
+import nose
+import sudoku
+import unittest
+
+
+def test_9x9_dimensions():
+    '''
+    Test dimenions of a 9x9 Sudoku board.
+    '''
+    b = sudoku.Board()
+    assert len(b.keys()) == 81
+    assert b.size == 9
+    assert b.box_size == 3
+    for square, values in b.items():
+        assert len(values) == 9
+
+
+def test_9x9_units():
+    '''
+    Test units of a 9x9 Sudoku board.
+    '''
+    b = sudoku.Board()
+    for r in range(b.size):
+        row = b.row(r)
+        assert len(row) == 9
+        for sq in row:
+            assert sq[1] == r
+
+    for c in range(b.size):
+        col = b.col(c)
+        assert len(col) == 9
+        for sq in col:
+            assert sq[0] == c
+
+    for x in range(0, b.size, b.box_size):
+        for y in range(0, b.size, b.box_size):
+            box = b.box(x, y)
+            assert len(box) == 9
+            # TODO: Finish this test
+
+def test_9x9_row():
+    '''
+    A few tests on rows of a 9x9 Sudoku board.
+    '''
+    b = sudoku.Board()
+    row = b.row(1)
+    expected_keys = ((x, 1) for x in range(b.size))
+    for ekey in expected_keys:
+    	assert ekey in row
+    # No negative numbers
+    assert (-1, 1) not in row
+    # Only squares with the right y-coordinate
+    assert (0, 0) not in row
+    # No keys above the size of the board
+    assert (b.size, 1) not in row
+
+
+def test_9x9_col():
+    '''
+    A few tests on rows of a 9x9 Sudoku board.
+    '''
+    b = sudoku.Board()
+    col = b.col(3)
+    expected_keys = ((3, y) for y in range(b.size))
+    for ekey in expected_keys:
+    	assert ekey in col
+    # No negative numbers
+    assert (3, -1) not in col
+    # Only squares with the right x-coordinate
+    assert (0, 0) not in col
+    # No keys above the size of the board
+    assert (3, b.size) not in col
+
+
+def test_9x9_box():
+    '''
+    A few tests on boxes of a 9x9 Sudoku board.
+    '''
+    b = sudoku.Board()
+    assert True
+
+
+def test_9x9_peers():
+    '''
+    Test peers.
+    '''
+    b = sudoku.Board()
+    peers = b.peers(3, 3)
+    expected_peers = set(  [(x, 3) for x in range(b.size)]
+                         + [(3, y) for y in range(b.size)]
+                         + [(3, 3), (3, 4), (3, 5), (4, 3), (4, 4), (4, 5), (5, 3), (5, 4), (5, 5)])
+    expected_peers.remove((3, 3))
+    for epeer in expected_peers:
+    	assert epeer in peers, '{} not in peers of (3, 3)'.format(epeer)
+
+
+def test_9x9_str():
+    '''
+    Test string generation/printing.
+    '''
+    b = sudoku.Board()
+    expected_str = '\n'.join(['. . . | . . . | . . .',
+                              '. . . | . . . | . . .',
+                              '. . . | . . . | . . .',
+                              '------+-------+------',
+                              '. . . | . . . | . . .',
+                              '. . . | . . . | . . .',
+                              '. . . | . . . | . . .',
+                              '------+-------+------',
+                              '. . . | . . . | . . .',
+                              '. . . | . . . | . . .',
+                              '. . . | . . . | . . .'])
+    assert str(b) == expected_str
+
+
+def main():
+    nose.main()
+
+
+if __name__ == '__main__':
+    main()