title: NetLogo AgentSet substraction
body: <p>I got the error message: </p>
  
  <pre><code>MEMBER? expected input to be a string or list or agentset but got the number 0 instead.
  </code></pre>
  
  <p>during running following NetLogo Code:</p>
  
  <pre><code>to find-flockmates  ;; turtle reporter
    ;; latch on to the nearby birds
    set flockmates-infront other birds in-cone vision cone-infront-degree
    set flockmates-sidewise other birds in-cone vision cone-sidewise-degree
  
    ;; agentset substraction
    if (count flockmates-infront &gt; 0)[
      set flockmates-sidewise (flockmates-sidewise with [not member? self flockmates-infront])  
      ] 
  end
  </code></pre>
  
  <p>Can someone tell me what I am doing wrong or another possible solution for a substraction of two agentsets?</p>