diff --git a/lab2/ibspline.py b/lab2/ibspline.py
index 7c88030..f4f9eb2 100644
--- a/lab2/ibspline.py
+++ b/lab2/ibspline.py
@@ -20,6 +20,7 @@ def ibspline(inputA, inputB=None):
     global save_message_xloc
     global num_sample
     global curve_degree, knot_vector, add_cp_mode # added for Bspline
+    global ax_lr_button, lr_button # added for Lane-Riesenfeld
 
     # de Boor's algorithm to evaluate a point on a B-spline.
     # Returns (x, y) coordinate at parameter t
@@ -119,6 +120,7 @@ def ibspline(inputA, inputB=None):
         plt.plot(vX, vY, 'ob', picker=True, pickradius=5)
         return
 
+
     # Redraw the entire plot
     def redrawPlot(vX, vY):
         global text_message, ax
@@ -187,6 +189,58 @@ def ibspline(inputA, inputB=None):
     
     # CallbackS
     
+    # Lane-Riesenfeld subdivision callback
+    def lrSubdivideCallback(event):
+        global vX, vY, curve_degree, knot_vector
+        
+        if len(vX) == 0: return
+        
+        # Check if knot vector is uniform
+        is_uniform = True
+        if len(knot_vector) > 1:
+            diff = knot_vector[1] - knot_vector[0]
+            for i in range(1, len(knot_vector) - 1):
+                if abs((knot_vector[i+1] - knot_vector[i]) - diff) > 1e-5:
+                    is_uniform = False
+                    break
+                    
+        if not is_uniform:
+            outputPlotMessage("Error: LR-Subdivide requires uniform knot distances.")
+            plt.draw()
+            return
+            
+        n = curve_degree
+        m = len(vX)
+        points = list(zip(vX, vY))
+        
+        # Step 1: Double the points (P0, P0, P1, P1, ...)
+        doubled_points = []
+        for p in points:
+            doubled_points.append(p)
+            doubled_points.append(p)
+            
+        # Step 2: Apply moving average n times
+        for _ in range(n):
+            smoothed_points = []
+            # Average adjacent points
+            for i in range(len(doubled_points) - 1):
+                px = (doubled_points[i][0] + doubled_points[i+1][0]) / 2.0
+                py = (doubled_points[i][1] + doubled_points[i+1][1]) / 2.0
+                smoothed_points.append((px, py))
+            doubled_points = smoothed_points
+            
+        # Update vX and vY
+        vX = [p[0] for p in doubled_points]
+        vY = [p[1] for p in doubled_points]
+        
+        # update knot : maintain uniformity but increase density
+        new_m = len(vX)
+        knot_vector = list(range(1, new_m + curve_degree + 1))
+        
+        outputPlotMessage(f"LR-Subdivide applied. (m={len(vX)})")
+        redrawPlot(vX, vY)
+        return
+    
     # callback of add cp
     def addCPButtonCallback(event):
         global add_cp_mode
@@ -265,6 +319,7 @@ def ibspline(inputA, inputB=None):
     def createButtons(left_pos, button_width, button_height):
         global ax_add_button, add_button
         global ax_save_button, save_button
+        global ax_lr_button, lr_button
 
         # Colors
         inactive_color = 'lightgray' 
@@ -276,6 +331,13 @@ def ibspline(inputA, inputB=None):
         add_button.color = inactive_color
         add_button.hovercolor = inactive_color
 
+        # LR-Subdivide
+        ax_lr_button = plt.axes([left_pos, 0.7, button_width, button_height])
+        lr_button = Button(ax_lr_button, "LR-Sub")
+        lr_button.on_clicked(lrSubdivideCallback)
+        lr_button.color = inactive_color
+        lr_button.hovercolor = inactive_color
+
         # Save
         ax_save_button = plt.axes([left_pos, 0.6, button_width, button_height])
         save_button = Button(ax_save_button, "Save")
@@ -288,10 +350,12 @@ def ibspline(inputA, inputB=None):
 
     # not enable all buttons as smooth needs subdivision first
     def enableButtons():
-        global add_button, save_button
+        global add_button, save_button, lr_button
 
         add_button.color = 'white'
         add_button.hovercolor = 'green'
+        lr_button.color = 'white'
+        lr_button.hovercolor = 'green'
         save_button.color = 'white'
         save_button.hovercolor = 'green'
         plt.draw()