part 1
------
    +-----+              +---------------+
 a1 |  ---|------------->| 1 | 2 | 3 | 4 |
    +-----+        /---->+---------------+
                   |
    +-----+        |
 a2 |  ---|--------/
    +-----+


    +-----+              +---------------+
 b1 |  ---|------------->| 1 | 2 | 3 | 4 |
    +-----+              +---------------+

    +-----+              +---------------+
 b2 |  ---|------------->| 1 | 2 | 3 | 4 |
    +-----+              +---------------+


part 2
------
true 

part 3
------
false


part 4
------

Before the call we have:

+--------------+
| main         |
| ----         |
|       +----+ |              +---------------+
|    a1 |  --|-|------------->| 1 | 2 | 3 | 4 |
|       +----+ |              +---------------+
+--------------+


At the start of the call we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |
| vals2 |    | |
|       +----+ |
|       +----+ |
|  vals |  --|-|---+
|       +----+ |   |
+--------------+   |
| main         |   |
| ----         |   |
|       +----+ |   +--------->+---------------+
|    a1 |  --|-+------------->| 1 | 2 | 3 | 4 |
|       +----+ |              +---------------+
+--------------+


After the first for loop, we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |
| vals2 |    | |
|       +----+ |
|       +----+ |
|  vals |  --|-|---+
|       +----+ |   |
+--------------+   |
| main         |   |
| ----         |   |
|       +----+ |   +--------->+---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+


After the creation of vals2, we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |              +---------------+
| vals2 |  --|-|------------->| 0 | 0 | 0 | 0 |
|       +----+ |              +---------------+
|       +----+ |
|  vals |  --|-|---+
|       +----+ |   |
+--------------+   |
| main         |   |
| ----         |   |
|       +----+ |   +--------->+---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+


After the second loop, we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |              +---------------+
| vals2 |  --|-|------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
|       +----+ |
|  vals |  --|-|---+
|       +----+ |   |
+--------------+   |
| main         |   |
| ----         |   |
|       +----+ |   +--------->+---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+


After the assignment vals = vals2, we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |              +---------------+
| vals2 |  --|-|------------->|-1 |-2 |-3 |-4 |
|       +----+ |   +--------->+---------------+
|       +----+ |   |
|  vals |  --|-|---+
|       +----+ |    
+--------------+    
| main         |    
| ----         |    
|       +----+ |              +---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+


After the second loop, we have:

+--------------+
| mystery      |
| -------      |
|       +----+ |              +---------------+
| vals2 |  --|-|------------->| 1 | 0 |-1 |-2 |
|       +----+ |   +--------->+---------------+
|       +----+ |   |
|  vals |  --|-|---+
|       +----+ |    
+--------------+    
| main         |    
| ----         |    
|       +----+ |              +---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+


After the method call completes, we have:

+--------------+    
| main         |    
| ----         |    
|       +----+ |              +---------------+
|    a1 |  --|-+------------->|-1 |-2 |-3 |-4 |
|       +----+ |              +---------------+
+--------------+