title: jQuery Validate - Multiple Input fields - some are required
body: <p>I have the following problem:</p>
  
  <p>I got a form with 3 input fields type number. I want at all time that only 2 to be required. So if Input A and input B are filled in input C is disabled. But when the user clears input A, input C must be available. etc.. so 2 must be filled in, there is no matter which two ! </p>
  
  <p>I'm making a small application for the "theory of pythagoras" where you can fill in two sides. Doesn't matter which 2 sides. </p>
  
  <pre><code>&lt;div class="selector"&gt;
      &lt;input type="number" placeholder="A" name="A" id="A"&gt;
      &lt;input type="number" placeholder="B" name="B" id="B"&gt;
      &lt;input type="number" placeholder="C" name="C" id="C"&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>jQuery Validation:</p>
  
  <pre><code>$(".selector").validate({
    rules: {
      // simple rule, converted to {required:true}
      A: "required",
      B: "required",
      C: "required"
    }
  });
  </code></pre>
  
  <p>who can help me !</p>