===============================================================================
Steps [5] through [7] (atop [0] through [4]
===============================================================================
   
class Problem7
+-------------------------------------------------------------------+
|      +---+      +---+      +---+      +---+      +---+      +---+ |
| args | *-+-+ F1 | * |   F2 | * |   B1 | * |   B2 | * |   B3 |   | |
|      +---+ |    +-+-+      +-+-+      +-+-+      +-+-+      +---+ |
+------------+------+----------+----------+----------+--------------+
             |      |          |          |          | 
      <------+      | [1]      | [2]  [3] +--+   [4] +------+
class Frippy        |          |             |              |
+-------------------+----------+-------------+--------------+--------------+
|                   V          |             |              |              |
| +----------+   +----------+  >+----------+ | +----------+ | +----------+ |
| |   +----+ |   |   +----+ |   |   +----+ | | |   +----+ | | |   +----+ | |
| | x |    | |   | x |0   | |   | x |0   | | | | x |0   | | | | x |    | | |
| |   +----+ |   |   +----+ |   |   +----+ | | |   +----+ | | |   +----+ | |
| |          |   |          |   |     [7]  | | |          | | |          | |
| |   +----+ |   |   +----+ |   |   +-\-/+ | | |   +----+ | | |   +----+ | |
| | F |    | |   | F |null| |   | F |nuXl*-+-+>| F |null| | | | F |    | | |
| |   +----+ |   |   +----+ |   |   +-/-\+ | | |   +----+ | | |   +----+ | |
| +----------+   +----------+   +----------+ | +----------+ | +----------+ |
|                                            |        ^     |              |
+--------------------------------------------+--------+-----+--------------+
                                             |        |     |
                                             |    [6] |     |
class Boingo                                 |        |     |
+--------------------------------------------+--------|-----+--------------+
|                                            |        |     |              |
| +----------+   +----------+   +----------+ +>+------|---+ +>+----------+ |
| |   +----+ |   |   +----+ |   |   +----+ |   |   +--|-+ |   |   +-\-/+ | |
| | a |    | |   | a |    | |   | a |    | |   | a |nu|l| |   | a |nuXl*-+-+-+
| |   +----+ |   |   +----+ |   |   +----+ |   |   +--|-+ |   |   +-/-\+ | | |
| |          |   |          |   |          |   |      |   |   |          | | |
| |   +----+ |   |   +----+ |   |   +----+ |   |   +-\*/+ |   |   +----+ | | |
| | b |    | |   | b |    | |   | b |    | |   | b |nuXl| |   | b |null| | | |
| |   +----+ |   |   +----+ |   |   +----+ |   |   +-/-\+ |   |   +----+ | | |
| +----------+   +----------+   +----------+   +----------+   +----------+ | |
|                                                                          | |
+--------------------------------------------------------------------------+ |
                                                                             |
class String                                                                 |
+----------------------+                                                     |
|                      |                [5]                                  |
| "grok"<--------------+-----------------------------------------------------+
|                      |
+----------------------+