title: How to find node with no incoming relationship in neo4j
body: <p>I am having 2 node types lets say of type 'Student' and 'Teacher'</p>
  
  <pre><code>Student have {id, name}.
  Teacher have {id, name}.
  </code></pre>
  
  <p>Student can have optional relationship with Class node as 'TEACHES'.</p>
  
  <pre><code>(t:Teacher)-[r:TEACHES]-&gt;(c:Student).
  
  [r:TEACHES] - Optional relationship. (present or may not present)
  </code></pre>
  
  <p>I want to find "Student" nodes who don't have teacher. i.e There is no any incoming relationship "TEACHES"</p>
  
  <p>Please help.</p>