title: Prolog how to prevent repetitive answers
body: <p>For my program the Knowledge Base has atomic statements and rules such as</p>
  
  <pre><code>store(itemName, ProductType)
  </code></pre>
  
  <p>ex: store(iPhone5, phone)</p>
  
  <pre><code>manufacturer(itemName, Company)
  </code></pre>
  
  <p>ex: manufacturer(iPhone5, apple)</p>
  
  <p>query is to find out if there is a company that manufacturered more than 2 distinct product types, so for apple there would be Macbook, iPad, and iPhone</p>
  
  <p>Here is our query:</p>
  
  <p><code>?- store(ItemID1, ProductType1), manufacturer(ItemID1, Company), store(ItemID2,     ProductType2), manufacturer(ItemID2, Company), store(ItemID3, ProductType3), manufacturer(ItemID3, Company), not ProductType1 = ProductType2, not ProductType1 = ProductType3, not ProductType2 = ProductType3.</code></p>
  
  <p>It gives the correct answer listing 3 apple products but pressing more gives the same answer again and again. Is there a way to stop this?</p>
  
  <p>Note: I am aware of the other answers to other questions given on this site but don't know how to implement them given my limited knowledge of Prolog and not sure if those answers apply to this question.</p>
  
  <p>Note: For this question I am not allowed to use <code>!</code> <code>-&gt;</code> and <code>;</code> operators </p>