title: Is Project Reactor flatMap order sequential?
body: <p>Is flatMap on Flux always sequential?
  I know that It is not sequential when then function used in flatMap return flux.
  <a href="https://projectreactor.io/docs/core/release/api/reactor/core/publisher/Flux.html#flatMap-java.util.function.Function-" rel="nofollow noreferrer">project-reactor flatMap</a></p>
  <p>But if the function used in flatMap returns mono, would it be always sequential?</p>
  <p>Say I have a function that takes an object and returns only Mono.</p>
  <pre class="lang-kotlin prettyprint-override"><code>fun aFunction(foo: Int): Mono&lt;Int&gt; {
      return (foo + 1).toMono()
  }
  </code></pre>
  <p>then</p>
  <pre class="lang-kotlin prettyprint-override"><code>Flux.just(1,2,3,4)
      .flatMap{ aFunction(it) }
  </code></pre>
  <p>always return 2,3,4,5?</p>