title: Prolog programm returns yes instead of value
body: <p>I got the following event: <strong>item(C,X,G,P)</strong>, (<em>where <code>C</code> is a number for the product,<code>X</code> it's name,<code>G</code> it's price,<code>P</code> it's cost</em>).<br>
  When i use the command <strong><code>item(n3001,_,_,P)</code></strong> directly on the prolog console i get as answer<br>
  <code>G = 1.25 X = 100</code> but when i write the equation <code>p3(C)-: item(C,_,_,P).</code> then i consult the text i get as answer <code>yes</code>.<br>
    My question clarified is how come the one time i get the value of <code>P</code> which i want and the other time i get whether it's true or false?</p>