X (G-Y) = Node X in generation Y

1 (G0)
|         +------------------------+        +--------------------------+
+-------> |                        |        |                          |
          | Add (G-max(0, 0)+1=G1) | +----> | Add (G-max(1, 0)+1 = G2) |
+-------> |                        |        |                          |
|         +------------------------+        +--------------------------+
2 (G0)
                                                        ^
                                                        |
                                                        |
                                                        +

                                                        3 (G0)