anchor.diff:  3. _request / reply_: the message is sent to a single _consumer_ and let it _reply_ to the message by sending another
   _message_ to the initial sender
   
  -Ok, let's step back a minute because that's a lot of information to process... Why would you use Vert.x ? Vert.x is
  +Wao!, that's a lot of information to process... However, you might still want to ask: **What kind of applications can I use Vert.x for?** We say, Vert.x is
   incredibly flexible - whether it's simple network utilities, sophisticated modern web applications, HTTP/REST
   microservices, high volume event processing or a full blown backend message-bus application, Vert.x is a great fit.
  -It's fast, and does not constraint you. Last but not least, Vert.x will let you built a reactive system; in other
  -words: _responsive, elastic, resilient and asynchronous_!
  +It's fast, and does not constraint you. Last but not least, Vert.x provides appropriate tools to build reactive systems; sytems that are: _responsive, elastic, resilient and asynchronous_!
   
   
  
positive.code: 
  The main differences between these 2 codes are:
  
  * the first one is blocking and synchronous: the instructions are executed in _order_, but it may block the thread
  for a long time (because the web site may be slow or whatever).
  * the Vert.x one is asynchronous and non-blocking: the thread (event loop) is released while the connection with the
  HTTP server is established and so can do something else. When the response has been received, the **same** event loop
   calls the _callback_. Most of the Vert.x components are single-threaded (access only by a single thread), so no
   concurrency burden anymore. By the way, with Vert.x, even the DNS resolution is asynchronous and non-blocking (while
   Java DNS resolution is blocking).
  
  Another important point about the Vert.x description given above is _"on the JVM"_. Vert.x applications run on
  the Java Virtual Machine (8+), but that does not mean they have to be developed using the Java language. Vert.x
  applications can be developed in Java of course, but also in Groovy, in Ceylon, in Ruby, in JavaScript, or mix all these
  languages. This polyglot aspect lets you use the most appropriate language for the task.
  
  Vert.x lets you implement distributed applications, either by using the built-in TCP and HTTP server and client, but
  also using the Vert.x event bus, a lightweight mechanism to send and receive messages. With the event bus, you send
  
negative.code: in.close();
  ----
  
  But with Vert.x we are more likely to do:
  
  [source, java]
  -----
  