title: Implement the member predicate as a one-liner
body: <p>Interview question!</p>
  
  <p>This is how you normally define the <code>member</code> relation in Prolog:</p>
  
  <pre><code>member(X, [X|_]).        % member(X, [Head|Tail]) is true if X = Head 
                           % that is, if X is the head of the list
  member(X, [_|Tail]) :-   % or if X is a member of Tail,
    member(X, Tail).       % ie. if member(X, Tail) is true.
  </code></pre>
  
  <p>Define it using only one rule.</p>