+---+    +---+          |                +---+    +---+
      | a |    | b |          |                | a |    | b |
      +---+    +---+          |                +---+    +---+
        |        |            |                  |        |
        v        v            |                  v        v
      +---+    +---+          |                +------------+
      | c |--->| d |          |                |  synthetic |
      +---+    +---+          |                +------------+
        ^        |            |               /   |      |   \
        |        |            |              /    |      |    \
        |        v            |             v     v      v     v
      +---+    +---+          |          +---+  +---+  +---+  +---+
      | f |<---| e |          |          | f |  | c |  | d |  | e |
      +---+    +---+          |          +---+  +---+  +---+  +---+
        |        |            |            |                    |
        v        v            |            v                    v
      +---+    +---+          |          +---+                +---+
      | g |    | h |          |          | g |                | h |
      +---+    +---+          |          +---+                +---+

         Before                                     After
      Transformation                           Transformation