sequenceDiagram
    autonumber
    Alice->>Bob: Hello
    Bob->>Bob: Think
    Bob-->>Alice: Hi
    Alice->>Bob: Bye
---
+-------+     +-----+
| Alice |     | Bob |
+---+---+     +--+--+
    |            |
    | 1. Hello   |
    +----------->|
    |            |
    |            | 2. Think
    |            +--+
    |            |  |
    |            |<-+
    |            |
    | 3. Hi      |
    |<...........+
    |            |
    | 4. Bye     |
    +----------->|
    |            |
