diff --git a/src/board.rs b/src/board.rs
index 3e1702e..ea28e04 100644
--- a/src/board.rs
+++ b/src/board.rs
@@ -44,9 +44,9 @@ impl Board {
 
     /**
     Set the value of a tile, or removes it if `None` is given.
-    
+
     Returns the previous value or `None`.
-    
+
     Panics if `x` or `y` are beyond the boards dimensions or `value` is greater or equal to `num_options`.
     */
     pub fn set_tile(&mut self, x: usize, y: usize, value: Option<usize>) -> Option<usize> {
@@ -63,7 +63,7 @@ impl Board {
 
     /**
     Get the value of a tile, or `None` if no value is known.
-    
+
     Panics if `x` or `y` are beyond the boards dimensions.
     */
     pub fn get_tile(&self, x: usize, y: usize) -> Option<usize> {
diff --git a/src/constrain.rs b/src/constrain.rs
index 39fabdf..c00964b 100644
--- a/src/constrain.rs
+++ b/src/constrain.rs
@@ -47,7 +47,7 @@ fn _constrain_board(
                 valid.retain(|&opt| {
                     board.set_tile(x, y, Some(opt));
 
-                    check_fn(&board)
+                    check_fn(board)
                 });
                 log::trace!("still valid {valid:?}");
 
diff --git a/src/main.rs b/src/main.rs
index 1322a5e..a29c7b0 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -6,35 +6,35 @@ fn main() {
     simple_logger::init_with_level(log::Level::Info).unwrap();
 
     let mut board = board::Board::new(9, 9, 9);
-    board.set_tile(0, 1, Some(6 -1));
-    board.set_tile(0, 2, Some(8 -1));
-    board.set_tile(0, 4, Some(3 -1));
-    board.set_tile(0, 7, Some(7 -1));
-    board.set_tile(1, 0, Some(2 -1));
-    board.set_tile(1, 3, Some(9 -1));
-    board.set_tile(1, 6, Some(1 -1));
-    board.set_tile(2, 1, Some(4 -1));
-    board.set_tile(2, 4, Some(8 -1));
-    board.set_tile(2, 5, Some(1 -1));
-    board.set_tile(2, 8, Some(3 -1));
-    board.set_tile(3, 2, Some(7 -1));
-    board.set_tile(3, 6, Some(4 -1));
-    board.set_tile(4, 3, Some(8 -1));
-    board.set_tile(4, 4, Some(1 -1));
-    board.set_tile(4, 5, Some(9 -1));
-    board.set_tile(5, 2, Some(9 -1));
-    board.set_tile(5, 6, Some(2 -1));
-    board.set_tile(6, 0, Some(7 -1));
-    board.set_tile(6, 3, Some(3 -1));
-    board.set_tile(6, 4, Some(9 -1));
-    board.set_tile(6, 7, Some(4 -1));
-    board.set_tile(7, 2, Some(2 -1));
-    board.set_tile(7, 5, Some(5 -1));
-    board.set_tile(7, 8, Some(6 -1));
-    board.set_tile(8, 1, Some(3 -1));
-    board.set_tile(8, 4, Some(7 -1));
-    board.set_tile(8, 6, Some(9 -1));
-    board.set_tile(8, 7, Some(5 -1));
+    board.set_tile(0, 1, Some(6 - 1));
+    board.set_tile(0, 2, Some(8 - 1));
+    board.set_tile(0, 4, Some(3 - 1));
+    board.set_tile(0, 7, Some(7 - 1));
+    board.set_tile(1, 0, Some(2 - 1));
+    board.set_tile(1, 3, Some(9 - 1));
+    board.set_tile(1, 6, Some(1 - 1));
+    board.set_tile(2, 1, Some(4 - 1));
+    board.set_tile(2, 4, Some(8 - 1));
+    board.set_tile(2, 5, Some(1 - 1));
+    board.set_tile(2, 8, Some(3 - 1));
+    board.set_tile(3, 2, Some(7 - 1));
+    board.set_tile(3, 6, Some(4 - 1));
+    board.set_tile(4, 3, Some(8 - 1));
+    board.set_tile(4, 4, Some(1 - 1));
+    board.set_tile(4, 5, Some(9 - 1));
+    board.set_tile(5, 2, Some(9 - 1));
+    board.set_tile(5, 6, Some(2 - 1));
+    board.set_tile(6, 0, Some(7 - 1));
+    board.set_tile(6, 3, Some(3 - 1));
+    board.set_tile(6, 4, Some(9 - 1));
+    board.set_tile(6, 7, Some(4 - 1));
+    board.set_tile(7, 2, Some(2 - 1));
+    board.set_tile(7, 5, Some(5 - 1));
+    board.set_tile(7, 8, Some(6 - 1));
+    board.set_tile(8, 1, Some(3 - 1));
+    board.set_tile(8, 4, Some(7 - 1));
+    board.set_tile(8, 6, Some(9 - 1));
+    board.set_tile(8, 7, Some(5 - 1));
 
     if constrain::constrain_board(&mut board, &rules::valid_board_sudoku) {
         println!("{board}");
diff --git a/src/rules.rs b/src/rules.rs
index f8599a8..3e3634a 100644
--- a/src/rules.rs
+++ b/src/rules.rs
@@ -98,8 +98,8 @@ pub fn valid_board_sudoku(board: &Board) -> bool {
     }
 
     // check 3x3 cells: must be unique
-    for x in [0,3,6] {
-        for y in [0,3,6] {
+    for x in [0, 3, 6] {
+        for y in [0, 3, 6] {
             let mut set = HashSet::new();
             if !get_cell(board, x, y)
                 .iter()