diff --git a/src/board.rs b/src/board.rs
index 4a2396c..41d926d 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -14,8 +14,8 @@ impl Board {
             panic!("Input string not length 81: got {}", str.len())
         }
         let mut squares = Vec::new();
-        for c in str.chars() {
-            squares.push(Square::from_char(c));
+        for (i, c) in str.chars().enumerate() {
+            squares.push(Square::from_char(i as u8, c));
         }
         let mut board = Board {
             squares: squares.try_into().unwrap(),
@@ -26,44 +26,44 @@ impl Board {
 
     pub fn restrict_marks(&mut self) {
         let self_copy = self.clone();
-        for (index, ref mut square) in self.squares.iter_mut().enumerate() {
-            if let Square::Marks(ref mut marks) = square {
-                self_copy.row_from_index(index).values().for_each(|value| {
+        for ref mut square in self.squares.iter_mut() {
+            if let Square::Marks(index, ref mut marks) = square {
+                self_copy.row_from_index(*index).values().for_each(|value| {
                     marks.set(value as usize, false);
                 });
-                self_copy.col_from_index(index).values().for_each(|value| {
+                self_copy.col_from_index(*index).values().for_each(|value| {
                     marks.set(value as usize, false);
                 });
-                self_copy.box_from_index(index).values().for_each(|value| {
+                self_copy.box_from_index(*index).values().for_each(|value| {
                     marks.set(value as usize, false);
                 });
             }
         }
     }
 
-    pub fn row_from_index(&self, index: usize) -> SquareIter {
+    pub fn row_from_index(&self, index: u8) -> SquareIter {
         SquareIter::from_row(&self.squares, index / 9)
     }
 
-    pub fn row(&self, row: usize) -> SquareIter {
+    pub fn row(&self, row: u8) -> SquareIter {
         SquareIter::from_row(&self.squares, row)
     }
 
-    pub fn col_from_index(&self, index: usize) -> SquareIter {
+    pub fn col_from_index(&self, index: u8) -> SquareIter {
         SquareIter::from_col(&self.squares, index % 9)
     }
 
-    pub fn col(&self, col: usize) -> SquareIter {
+    pub fn col(&self, col: u8) -> SquareIter {
         SquareIter::from_col(&self.squares, col)
     }
 
-    pub fn box_from_index(&self, index: usize) -> SquareIter {
+    pub fn box_from_index(&self, index: u8) -> SquareIter {
         let row = index / 27;
         let col = (index % 9) / 3;
         SquareIter::from_box(&self.squares, (row * 3) + col)
     }
 
-    pub fn boxn(&self, boxn: usize) -> SquareIter {
+    pub fn boxn(&self, boxn: u8) -> SquareIter {
         SquareIter::from_box(&self.squares, boxn)
     }
 
@@ -71,7 +71,7 @@ impl Board {
         self.squares
             .iter()
             .map(|sq| match sq {
-                Square::Value(x) => x.to_string(),
+                Square::Value(_, x) => x.to_string(),
                 _ => ".".to_string(),
             })
             .fold(String::new(), |a, b| a + &b)
@@ -81,15 +81,10 @@ impl Board {
         self.squares
             .iter()
             .map(|sq| match sq {
-                Square::Marks(marks) => {
-                    marks
-                        .into_iter()
-                        .map(|a| a + 1)
-                        .fold(String::new(), |mut a, b| {
-                            a.push_str(&b.to_string());
-                            a
-                        })
-                }
+                Square::Marks(_, marks) => marks.into_iter().fold(String::new(), |mut a, b| {
+                    a.push_str(&b.to_string());
+                    a
+                }),
                 _ => String::new(),
             })
             .fold(String::new(), |mut a, b| {
diff --git a/src/iterators.rs b/src/iterators.rs
index 1bed6f1..f16a2d6 100644
--- a/src/iterators.rs
+++ b/src/iterators.rs
@@ -53,39 +53,50 @@ pub struct SquareIter {
 }
 
 impl SquareIter {
-    pub fn from_row(squares: &[Square; 81], row: usize) -> SquareIter {
+    pub fn from_row(squares: &[Square; 81], row: u8) -> SquareIter {
         SquareIter {
-            squares: to_row(squares, row),
+            squares: to_row(squares, row as usize),
             curr: 0,
         }
     }
 
-    pub fn from_col(squares: &[Square; 81], col: usize) -> SquareIter {
+    pub fn from_col(squares: &[Square; 81], col: u8) -> SquareIter {
         SquareIter {
-            squares: to_col(squares, col),
+            squares: to_col(squares, col as usize),
             curr: 0,
         }
     }
 
-    pub fn from_box(squares: &[Square; 81], boxn: usize) -> SquareIter {
+    pub fn from_box(squares: &[Square; 81], boxn: u8) -> SquareIter {
         SquareIter {
-            squares: to_box(squares, boxn),
+            squares: to_box(squares, boxn as usize),
             curr: 0,
         }
     }
 
-    pub fn values(self) -> std::iter::FilterMap<SquareIter, impl FnMut(Square) -> Option<u8>> {
+    pub fn values_enumerate(
+        self,
+    ) -> std::iter::FilterMap<SquareIter, impl FnMut(Square) -> Option<(u8, u8)>> {
         self.filter_map(|sq| match sq {
-            Square::Value(v) => Some(v),
+            Square::Value(i, v) => Some((i, v)),
             _ => None,
         })
     }
 
+    pub fn values(
+        self,
+    ) -> std::iter::Map<
+        std::iter::FilterMap<SquareIter, impl FnMut(Square) -> Option<(u8, u8)>>,
+        impl FnMut((u8, u8)) -> u8,
+    > {
+        self.values_enumerate().map(|(i, v)| v)
+    }
+
     pub fn marks(
         self,
     ) -> std::iter::FilterMap<SquareIter, impl FnMut(Square) -> Option<Bitmap<10>>> {
         self.filter_map(|sq| match sq {
-            Square::Marks(m) => Some(m),
+            Square::Marks(_, m) => Some(m),
             _ => None,
         })
     }
diff --git a/src/main.rs b/src/main.rs
index d8a3adb..e1af7a0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -7,7 +7,6 @@ mod validator;
 use strategy::Strategy;
 
 fn main() {
-    /*
     let nyt_hard = "3...184.9\
                     8.47.....\
                     .....61..\
@@ -17,7 +16,7 @@ fn main() {
                     ...6.1...\
                     17.2.....\
                     5........";
-    */
+    /*
     let nyt_easy = "154..627.\
                     ..817..45\
                     ..649..1.\
@@ -27,7 +26,8 @@ fn main() {
                     5..9....3\
                     .97...1.2\
                     8...54...";
-    let mut sudoku_board = board::Board::from_string(nyt_easy);
+    */
+    let mut sudoku_board = board::Board::from_string(nyt_hard);
 
     if let validator::BoardState::Broken(ind) = validator::validate_board(&sudoku_board) {
         println!("{}", sudoku_board.to_url());
diff --git a/src/square.rs b/src/square.rs
index 675ccd7..9200cac 100644
--- a/src/square.rs
+++ b/src/square.rs
@@ -2,26 +2,26 @@ use bitmaps::Bitmap;
 
 #[derive(Clone, Debug)]
 pub enum Square {
-    Value(u8),
-    Marks(Bitmap<10>),
+    Value(u8, u8),
+    Marks(u8, Bitmap<10>),
 }
 
 impl Square {
-    pub fn from_char(c: char) -> Square {
+    pub fn from_char(index: u8, c: char) -> Square {
         match c {
-            '1' => Square::Value(1),
-            '2' => Square::Value(2),
-            '3' => Square::Value(3),
-            '4' => Square::Value(4),
-            '5' => Square::Value(5),
-            '6' => Square::Value(6),
-            '7' => Square::Value(7),
-            '8' => Square::Value(8),
-            '9' => Square::Value(9),
+            '1' => Square::Value(index, 1),
+            '2' => Square::Value(index, 2),
+            '3' => Square::Value(index, 3),
+            '4' => Square::Value(index, 4),
+            '5' => Square::Value(index, 5),
+            '6' => Square::Value(index, 6),
+            '7' => Square::Value(index, 7),
+            '8' => Square::Value(index, 8),
+            '9' => Square::Value(index, 9),
             '.' => {
                 let mut bm = Bitmap::mask(10);
                 bm.set(0, false);
-                Square::Marks(bm)
+                Square::Marks(index, bm)
             }
             _ => panic!("Unexpected character in input: {}", c),
         }
@@ -29,8 +29,8 @@ impl Square {
 
     pub fn to_str(&self) -> String {
         match self {
-            Square::Marks(_) => " ".to_string(),
-            Square::Value(v) => v.to_string(),
+            Square::Marks(_, _) => " ".to_string(),
+            Square::Value(_, v) => v.to_string(),
         }
     }
 }
diff --git a/src/strategy/naked_single.rs b/src/strategy/naked_single.rs
index 46d6ba7..c4730fb 100644
--- a/src/strategy/naked_single.rs
+++ b/src/strategy/naked_single.rs
@@ -1,7 +1,7 @@
 use crate::{board::Board, square::Square, strategy::Strategy};
 
 pub struct NakedSingle {
-    index: usize,
+    index: u8,
     value: u8,
 }
 
@@ -13,20 +13,19 @@ impl Strategy for NakedSingle {
         board
             .squares
             .iter()
-            .enumerate()
-            .filter_map(|(index, square)| match square {
-                Square::Marks(marks) => Some((index, marks)),
+            .filter_map(|square| match square {
+                Square::Marks(index, marks) => Some((index, marks)),
                 _ => None,
             })
             .find(|(_index, marks)| marks.len() == 1)
             .map(|(index, marks)| NakedSingle {
-                index,
+                index: *index,
                 value: marks.first_index().unwrap() as u8,
             })
     }
 
     fn apply(&self, mut board: Board) -> Board {
-        board.squares[self.index] = Square::Value(self.value);
+        board.squares[self.index as usize] = Square::Value(self.index, self.value);
         board.restrict_marks();
         board
     }
diff --git a/src/validator.rs b/src/validator.rs
index 71f8941..6fc95e7 100644
--- a/src/validator.rs
+++ b/src/validator.rs
@@ -6,45 +6,42 @@ pub enum BoardState {
     InProgress,
 }
 
-fn are_unique<T>(iter: T) -> bool
+fn check_unique<T>(iter: T) -> Option<BoardState>
 where
-    T: Iterator<Item = u8>,
+    T: Iterator<Item = (u8, u8)>,
 {
     let mut bitmap: bitmaps::Bitmap<10> = bitmaps::Bitmap::new();
 
-    for item in iter {
+    for (ind, item) in iter {
         if bitmap.get(item as usize) {
-            return false;
+            return Some(BoardState::Broken(ind));
         }
         bitmap.set(item as usize, true);
     }
-    true
+    None
 }
 
 pub fn validate_board(board: &Board) -> BoardState {
     for r in 0..9 {
-        if !are_unique(board.row(r).values()) {
-            // TODO: Add the index.
-            return BoardState::Broken(0);
+        if let Some(s) = check_unique(board.row(r).values_enumerate()) {
+            return s;
         }
     }
 
     for c in 0..9 {
-        if !are_unique(board.col(c).values()) {
-            // TODO: Add the index.
-            return BoardState::Broken(0);
+        if let Some(s) = check_unique(board.col(c).values_enumerate()) {
+            return s;
         }
     }
 
     for b in 0..9 {
-        if !are_unique(board.boxn(b).values()) {
-            // TODO: Add the index.
-            return BoardState::Broken(0);
+        if let Some(s) = check_unique(board.boxn(b).values_enumerate()) {
+            return s;
         }
     }
 
     if board.squares.iter().any(|sq| match sq {
-        Square::Marks(_) => true,
+        Square::Marks(..) => true,
         _ => false,
     }) {
         BoardState::InProgress