avoid lines that share the same endpoints, but in reverse order

src/Triangles.hs

@@ -69,11 +69,8 @@ combinations xs =
   . S.toList . S.fromList
   . filter (uncurry (/=))
   . sortOn (abs . uncurry distanceA)
-  -- . concat . withStrategy (parListChunk 2000 rdeepseq) $
+  . concatMap (\(x:xs) -> map (x,) xs)
-   $ [(x,y) | x <- xs, y <- xs]
+  . init . tails $ xs
-  -- . map (\x -> take edgeLengthThreshold .
-  --         sortOn (abs . uncurry distanceA)
-  -- . map (\y -> (min x y, max x y)) $ xs) $ xs
   where
     edgeLengthThreshold = 10