diff --git a/app/src/main/java/sudoku/Cell.java b/app/src/main/java/sudoku/Cell.java
index 336dcfc..674e8f3 100644
--- a/app/src/main/java/sudoku/Cell.java
+++ b/app/src/main/java/sudoku/Cell.java
@@ -36,4 +36,20 @@ public abstract class Cell {
 			return otherCell.getSymbolIndex() == this.getSymbolIndex();
 		return false;
 	}
+
+	@Override
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		sb.append("| ");
+		if (this.symbolIndex != NOSYMBOLE){
+			sb.append(this.symbolIndex);
+		}
+		else {
+			sb.append(" ");
+		}
+
+		sb.append(" |");
+		return sb.toString();
+	}
+
 }
diff --git a/app/src/main/java/sudoku/Coordinate.java b/app/src/main/java/sudoku/Coordinate.java
new file mode 100644
index 0000000..668dd85
--- /dev/null
+++ b/app/src/main/java/sudoku/Coordinate.java
@@ -0,0 +1,33 @@
+package sudoku;
+
+public class Coordinate {
+
+    private int x;
+    private int y;
+
+    public Coordinate(int row, int col) {
+        this.x = row;
+        this.y = col;
+    }
+
+    public int getX() {
+        return x;
+    }
+
+    public void setX(int x) {
+        this.x = x;
+    }
+
+    public int getY() {
+        return y;
+    }
+
+    public void setY(int y) {
+        this.y = y;
+    }
+
+    public int calculateIndex(int size) {
+        return this.y * size + this.x;
+    }
+
+}
diff --git a/app/src/main/java/sudoku/MultiDoku.java b/app/src/main/java/sudoku/MultiDoku.java
index 1e3a4e5..956f076 100644
--- a/app/src/main/java/sudoku/MultiDoku.java
+++ b/app/src/main/java/sudoku/MultiDoku.java
@@ -42,4 +42,20 @@ public class MultiDoku {
 		return mutableCells;
 	}
 
+	public void updateSymbolsPossibilities() throws Exception {
+		for (Sudoku sudoku : subGrids){
+			sudoku.updateSymbolsPossibilities();
+		}
+	}
+
+	@Override
+	public String toString() {
+		StringBuilder sb = new StringBuilder();
+		sb.append("Multidoku {");
+		for (Sudoku sudoku : subGrids){
+			sb.append("\n\t").append(sudoku.toString());
+		}
+		sb.append("\n}");
+		return sb.toString();
+	}
 }
diff --git a/app/src/main/java/sudoku/Sudoku.java b/app/src/main/java/sudoku/Sudoku.java
index 3e20761..80ab687 100644
--- a/app/src/main/java/sudoku/Sudoku.java
+++ b/app/src/main/java/sudoku/Sudoku.java
@@ -55,4 +55,64 @@ public class Sudoku {
 		}
 		return mutableCells;
 	}
+
+	public boolean contains(Cell cell) {
+		return this.cells.contains(cell);
+	}
+
+	private Coordinate getCoordinateCell(Cell c) throws Exception {
+		int x=0, y=0;
+		int size = this.getSize();
+
+		if (!this.contains(c)) {
+			throw new Exception("The given cell is not in this sudoku.");
+		}
+
+		for (Cell cell : this.cells) {
+			if (cell == c){
+				return new Coordinate(x, y);
+			}
+			if (x == size - 1){
+				y+=1;
+				x=0;
+			}
+			else {
+				x+=1;
+			}
+		}
+		return new Coordinate(x, y);
+	}
+
+    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);
+                }
+                constraint.getPossibleSymbols(this, coord.getX(), coord.getY());
+				if (cell.getPossibleSymbols().isEmpty()){
+					throw new Exception("Rollback bitch");
+				}
+			}
+		}
+	}
+
+	public String toString (){
+		StringBuilder sb = new StringBuilder();
+		sb.append("Sudoku {");
+		for (int i = 0; i < getSize(); i++) {
+			sb.append("\n\t");
+			for (int j = 0; j < getSize(); j++) {
+				Cell cell = getCell(i, j);
+				sb.append(cell.toString()).append(" ");
+			}
+		}
+		sb.append("\n}");
+		return sb.toString();
+	}
+
 }
diff --git a/app/src/main/java/sudoku/SudokuFactory.java b/app/src/main/java/sudoku/SudokuFactory.java
index 6dfed0f..dfb0222 100644
--- a/app/src/main/java/sudoku/SudokuFactory.java
+++ b/app/src/main/java/sudoku/SudokuFactory.java
@@ -38,10 +38,10 @@ public class SudokuFactory {
 		return blocs;
 	}
 
-	public static MultiDoku createBasicEmptyRectangleSudoku(int width, int height) {
-		int symbolCount = width * height;
+	public static MultiDoku createBasicEmptyRectangleSudoku(int widthBlock, int heightBlock) {
+		int symbolCount = widthBlock * heightBlock;
 		List<Cell> cases = initCells(symbolCount);
-		List<Block> blocs = initRectangleBlocs(cases, width, height);
+		List<Block> blocs = initRectangleBlocs(cases, widthBlock, heightBlock);
 		List<IConstraint> constraints = new ArrayList<>();
 		constraints.add(new ColumnConstraint());
 		constraints.add(new LineConstraint());
diff --git a/app/src/main/java/sudoku/solver/Solver.java b/app/src/main/java/sudoku/solver/Solver.java
index cc7b80c..b87425c 100644
--- a/app/src/main/java/sudoku/solver/Solver.java
+++ b/app/src/main/java/sudoku/solver/Solver.java
@@ -32,6 +32,11 @@ public class Solver {
                 int symbol = currentCell.getPossibleSymbols().get(0);
                 currentCell.setSymbolIndex(symbol);
                 stack.push(currentCell);
+                try {
+                    doku.updateSymbolsPossibilities();
+                } catch (Exception e) {
+                    //TODO rollback
+                }
                 //TODO check constraints integrity in sudoku