title: Retrieve data from database without printing
body: <p>How do I retrieve data from the database to use it in a condition, but I don't want to print it the console.
  Problem I am doing is to retrieve a child from a database whose parents age differ by 15 years. </p>
  
  <p>This is the code I am using which works and prints the year of both parents.</p>
  
  <pre><code>family(person(_,_,date(_,_,Year1),_),
         person(_,_,date(_,_,Year2),_),
         [person(Name,Surname,_,_)|Y]), abs(Year1-Year2) &gt;= 15.
  </code></pre>