title: Add loop edges in datalog (bddbddb)
body: <p>I have the following rules that find all the paths among a graph.</p>
  
  <pre><code>path(X,Y) :- edge(X,Y).
  path(X,Y) :- edge(X,Z), path(Z,Y).
  </code></pre>
  
  <p>But, I want also <strong>for each node n</strong>, to <strong>add the edge n->n</strong> if not already present. </p>
  
  <p>How can I do this without having any relation of the nodes?</p>