+                  |
+                  |
-                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+                  |
+        c         |
+                  |
+  a           a   |
+                  |
*                  |
+    f      f      |
+                  |
+ a             a  |
+        a         |
+                  |
+    b      b      |
+                  |
+                  |
*                  |
+                  |
+                  |
+                  |
+  a           a   |
+    1   1   1     |
+                  |
1                  |
+                  |
!                  |
+                  |