diff --git a/app/src/main/java/sudoku/Sudoku.java b/app/src/main/java/sudoku/Sudoku.java
index 686ad94..b8b4f8f 100644
--- a/app/src/main/java/sudoku/Sudoku.java
+++ b/app/src/main/java/sudoku/Sudoku.java
@@ -21,11 +21,21 @@ public class Sudoku {
 		this.constraints = constraints;
 	}
 
+	/**
+	 * @return wether the coords are in the sudoku
+	 */
+	public boolean isValidCoords(int x, int y) {
+		int index = y * getSize() + x;
+		return index < getSize() * getSize();
+	}
+
 	/**
 	 * Try to place a cell at the given coordinate
+	 * 
 	 * @return false if it can't be done
 	 */
 	public boolean setCellSymbol(int x, int y, int value) {
+		assert (isValidCoords(x, y));
 		for (IConstraint constraint : this.constraints) {
 			if (!constraint.canBePlaced(this, x, y, value)) {
 				return false;
@@ -41,7 +51,7 @@ public class Sudoku {
 
 	public Cell getCell(int x, int y) {
 		int index = y * getSize() + x;
-		assert(index < getSize() * getSize());
+		assert (isValidCoords(x, y));
 		return this.cells.get(index);
 	}
 
@@ -58,8 +68,8 @@ public class Sudoku {
 	}
 
 	public boolean isValid(List<IConstraint> constraints) {
-		//not implemented
-		//for eachcase check contraintes
+		// not implemented
+		// for eachcase check contraintes
 		return false;
 	}
 
@@ -74,7 +84,7 @@ public class Sudoku {
 	public List<MutableCell> getMutableCells() {
 		List<MutableCell> mutableCells = new ArrayList<>();
 		for (Cell cell : this.cells) {
-			if (cell instanceof MutableCell){
+			if (cell instanceof MutableCell) {
 				mutableCells.add((MutableCell) cell);
 			}
 		}
@@ -86,7 +96,7 @@ public class Sudoku {
 	}
 
 	private Coordinate getCoordinateCell(Cell c) throws Exception {
-		int x=0, y=0;
+		int x = 0, y = 0;
 		int size = this.getSize();
 
 		if (!this.contains(c)) {
@@ -94,43 +104,42 @@ public class Sudoku {
 		}
 
 		for (Cell cell : this.cells) {
-			if (cell == c){
+			if (cell == c) {
 				return new Coordinate(x, y);
 			}
-			if (x == size - 1){
-				y+=1;
-				x=0;
-			}
-			else {
-				x+=1;
+			if (x == size - 1) {
+				y += 1;
+				x = 0;
+			} else {
+				x += 1;
 			}
 		}
 		return new Coordinate(x, y);
 	}
 
-    public void updateSymbolsPossibilities() throws Exception {
+	public void updateSymbolsPossibilities() throws Exception {
 		for (IConstraint constraint : constraints) {
 			List<MutableCell> mutableCells = this.getMutableCells();
 			for (MutableCell cell : mutableCells) {
-                Coordinate coord = null;
-                try {
-                    coord = this.getCoordinateCell(cell);
-                } catch (Exception e) {
-                    throw new RuntimeException(e);
-                }
+				Coordinate coord = null;
+				try {
+					coord = this.getCoordinateCell(cell);
+				} catch (Exception e) {
+					throw new RuntimeException(e);
+				}
 				List<Integer> newPossibleSymbols = cell.getPossibleSymbols();
-                newPossibleSymbols.retainAll(constraint.getPossibleSymbols(this, coord.getX(), coord.getY()));
+				newPossibleSymbols.retainAll(constraint.getPossibleSymbols(this, coord.getX(), coord.getY()));
 
 				cell.setPossibleSymbols(newPossibleSymbols);
 
-				if (cell.getPossibleSymbols().isEmpty()){
+				if (cell.getPossibleSymbols().isEmpty()) {
 					throw new Exception("Rollback bitch");
 				}
 			}
 		}
 	}
 
-	public String toString () {
+	public String toString() {
 		StringBuilder sb = new StringBuilder();
 		sb.append("Sudoku {");
 		for (int i = 0; i < getSize(); i++) {