title: Constrain the number of in-/outgoing edges from/to vertex?
body: <p>Currently I have a <code>class A extends V</code> and a <code>class B extends E</code>.<br>
  Now I would like to constrain the number of <code>B</code> edges that go out of <code>A</code> to say 2.<br>
  Is this possible and if it is how can I accomplish this?<br>
  I could not find anything useful about this, only about <code>LINK</code> properties but I would like to use edges.</p>