diff --git a/src/main.rs b/src/main.rs
index f0b1e2b..820864e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -35,7 +35,7 @@ struct Args {
 
 	/// Create puzzle
     #[arg(long)]
-    puzzle: bool,
+    puzzle: Option<usize>,
 }
 
 
@@ -58,8 +58,8 @@ fn main() {
     	return
     }
 
-    let result = if args.puzzle {
-        solver.make_puzzle().map(|_| ())
+    let result = if let Some(difficulty) = args.puzzle {
+        solver.make_puzzle(difficulty).map(|_| ())
     } else {
         solver.solve(args.limit).map(|_| ())
     };
diff --git a/src/solver/mod.rs b/src/solver/mod.rs
index 80cef80..06890a4 100644
--- a/src/solver/mod.rs
+++ b/src/solver/mod.rs
@@ -139,30 +139,35 @@ impl Solver {
 		}
 	}
 
-    pub fn make_puzzle(&mut self) -> Result<(), WaveError> {
+    pub fn make_puzzle(&mut self, difficulty: usize) -> Result<(), WaveError> {
     	self.solve_display = false;
-    	println!("# generating full...");
+    	println!("\n# generating full...");
     	let _ = self.solve(None)?;
 
     	println!("\n\n# erasing cells...");
     	let mut rng = rand::thread_rng();
-    	
-    	let erase_cell = loop {
-    	    let pos = (rng.gen_range(1..=self.size), rng.gen_range(1..=self.size));
-    	    if let Some(state) = self.grid[pos.0][pos.1].get_state() {
-    	        self.grid[pos.0][pos.1].reset_state();
-    	        break (pos, state);
-    	    }
-    	};
 
-    	let blocking_cell = cell::BlockingCell {
-    	    state: erase_cell.1,
-    	    position: erase_cell.0,
-    	};
-    	
-       	self.propagate_backtrack(erase_cell.0, blocking_cell); // get min allowed state number
-		// while min state number < 2 => loop
+		let mut min_num_allowed = 1;
 
+		while min_num_allowed <= difficulty {    	
+	    	let erase_cell = loop {
+	    	    let pos = (rng.gen_range(0..self.size), rng.gen_range(0..self.size));
+	    	    if let Some(state) = self.grid[pos.0][pos.1].get_state() {
+	    	        self.grid[pos.0][pos.1].reset_state();
+	    	        break (pos, state);
+	    	    }
+	    	};
+	    	let blocking_cell = cell::BlockingCell {
+	    	    state: erase_cell.1,
+	    	    position: erase_cell.0,
+	    	};
+	       	min_num_allowed = self.propagate_backtrack(erase_cell.0, blocking_cell);
+			if min_num_allowed > difficulty {
+				let _ = self.grid[erase_cell.0.0][erase_cell.0.1].collapse(&cell::CollapseOption::Set(erase_cell.1));
+				//println!("put back ({},{}) to {}", erase_cell.0.0, erase_cell.0.1, erase_cell.1);
+				//self.propagate_collapse(erase_cell.0, blocking_cell);
+			}
+		}
        	
 		println!();
     	self.display(ui::DisplayMode::Full);
diff --git a/src/solver/sudoku.rs b/src/solver/sudoku.rs
index 1ab579d..9cc335e 100644
--- a/src/solver/sudoku.rs
+++ b/src/solver/sudoku.rs
@@ -74,7 +74,9 @@ impl Solver {
     	Ok(())
     }
 
-	pub fn propagate_backtrack(&mut self, cell_pos: (usize, usize), removed_cell: cell::BlockingCell) {
+	pub fn propagate_backtrack(&mut self, cell_pos: (usize, usize), removed_cell: cell::BlockingCell) -> usize {
+		let mut min_allowed_number = self.size;
+
 		for index in 0..self.size {
 			if index != cell_pos.0 {
 	    		self.grid[index][cell_pos.1].add_allowed(&removed_cell);
@@ -87,6 +89,12 @@ impl Solver {
 			if square_row != cell_pos.0 || square_column != cell_pos.1 {
 				self.grid[square_row][square_column].add_allowed(&removed_cell);
 			}
+			let num_allowed = self.grid[square_row][square_column].get_num_allowed();
+			if num_allowed < min_allowed_number {
+				min_allowed_number = num_allowed
+			}
     	}
+
+    	min_allowed_number
 	}
 }