diff --git a/src/corners.py b/src/corners.py
--- a/src/corners.py
+++ b/src/corners.py
@@ -44,6 +44,9 @@ class Corners:
   #  For four points ABCD, there are 24 possible permutations corresponding to the desired KLMN.
   #  When we relax the condition of K being the upper left one, we get six groups of four equivalent permutations. KLMN ~ LMNK ~ MNKL ~ NKLM.
   #  
+  #  We determine which of the points' triplets are oriented clockwise and which counter-clockwise (minus/plus in the table below)
+  #  and swap them so that all triangles turn counter-clockwise.
+  #  
   #  xxxx -> KLMN | ABC | ABD | ACD | BCD | index | swap
   #  ------------ | :-: | :-: | :-: | :-: | ----: | ----
   #  A BCD        |  +  |  +  |  +  |  +  |    15 | 0
@@ -69,7 +72,7 @@ class Corners:
     if any(x==0 for x in (abc,abd,acd,bcd)): return False # collinear degenerate
     
     swaps=[(1,3),(0,1),(1,2),(0,3),(2,3),(0,0)]
-    index=(8 if abc>0 else 0)+(4 if abd>0 else 0)+(2 if acd>0 else 0)+(1 if bcd>0 else 0)
+    index=(8 if abc>0 else 0)|(4 if abd>0 else 0)|(2 if acd>0 else 0)|(1 if bcd>0 else 0)
     if index%3!=0: return False # concave degenerate
     swap=swaps[index//3]
     
@@ -88,11 +91,3 @@ class Corners:
     self.corners=self.corners[kIndex:]+self.corners[:kIndex] # rotate the upper left corner to the first place
         
     return True # success
-
-# import itertools
-# points=[(10,8),(8,10),(12,10),(10,12)]
-# for perm in itertools.permutations(points):
-  # corn=Corners()
-  # for p in perm: corn.add(p[0],p[1])
-  # print(corn.canonizeOrder())
-  # print(corn.corners)