diff --git a/src/analyzer/corners.py b/src/analyzer/corners.py
--- a/src/analyzer/corners.py
+++ b/src/analyzer/corners.py
@@ -1,9 +1,13 @@
-from .epoint import EPoint
+import logging
+
+from .epoint import EPoint
+
+log=logging.getLogger(__name__)
 
 
 class Corners:
 	def __init__(self):
-		self.corners=[]
+		self._corners=[]
 
 	## Adds a new corner if there are less than four, replaces the closest otherwise.
 	def add(self,x,y):
@@ -13,18 +17,18 @@ class Corners:
 				# self.corners[i]=a
 				# return
 
-		if len(self.corners)<4: # add a new corner
-			self.corners.append(a)
+		if len(self._corners)<4: # add a new corner
+			self._corners.append(a)
 
-		if len(self.corners)<4:
+		if len(self._corners)<4:
 			return
 
 		index,minDist=0,float('inf') # replace the corner closest to the clicked point
-		for i,c in enumerate(self.corners):
+		for i,c in enumerate(self._corners):
 			if a.dist(c)<minDist:
 				index,minDist=i,a.dist(c)
 
-		self.corners[index]=a
+		self._corners[index]=a
 
 	## Order the corners (0,1,2,3) so they make a quadrangle with vertices KLMN in counter-clockwise order, K being in the upper left.
 	#
@@ -48,9 +52,9 @@ class Corners:
 	#
 	#  @return True for a convex quadrangle, False for concave and degenerate cases.
 	def canonizeOrder(self):
-		if len(self.corners)!=4: return False # erroneus call
+		if len(self._corners)!=4: return False # erroneus call
 
-		a,b,c,d=self.corners
+		a,b,c,d=self._corners
 		abc=doubleTriangleArea(a,b,c)
 		abd=doubleTriangleArea(a,b,d)
 		acd=doubleTriangleArea(a,c,d)
@@ -63,24 +67,31 @@ class Corners:
 		if index%3!=0: return False # concave degenerate
 		swap=swaps[index//3]
 
-		self.corners[swap[0]], self.corners[swap[1]] = self.corners[swap[1]], self.corners[swap[0]] # counter-clockwise order
+		self._corners[swap[0]], self._corners[swap[1]] = self._corners[swap[1]], self._corners[swap[0]] # counter-clockwise order
 
 		kIndex=None
 		lowestSlope=float("inf")
 
-		for i,corner in enumerate(self.corners): # find the NK edge: going right-left with the lowest slope, secondarily the one going down
+		for i,corner in enumerate(self._corners): # find the NK edge: going right-left with the lowest slope, secondarily the one going down
 			ii=(i+1)%4
-			slope=abs(getSlope(corner,self.corners[ii]))
-			if corner.x>self.corners[ii].x and (slope<lowestSlope or (slope==lowestSlope and corner.y<self.corners[ii].y)):
+			slope=abs(getSlope(corner, self._corners[ii]))
+			if corner.x>self._corners[ii].x and (slope < lowestSlope or (slope == lowestSlope and corner.y < self._corners[ii].y)):
 				kIndex=ii
 				lowestSlope=slope
 
-		self.corners=self.corners[kIndex:]+self.corners[:kIndex] # rotate the upper left corner to the first place
+		self._corners= self._corners[kIndex:] + self._corners[:kIndex] # rotate the upper left corner to the first place
 
+		log.debug(self._corners)
 		return True # success
 
 	def scale(self,scale):
-		self.corners=[c*scale for c in self.corners]
+		self._corners=[c * scale for c in self._corners]
+
+	def __iter__(self):
+		return iter(self._corners)
+
+	def __len__(self):
+		return len(self._corners)
 
 
 ## Computes twice the area of the triangle formed by points a,b,c.