y tricky decisions once you&#39;d realised that you need to make them, but it would be very easy to implement the operators in a simplistic way without thinking about such things. (I&#39;d probably have done so if it weren&#39;t for the comments around Sum this morning.)</p>  <h3>What are we going to test?</h3>  <p>I&#39;ve only got in-depth tests for the int overloads, covering:</p>  <ul>   <li>Argument validation </li>    <li>Empty sequences for nullable and non-nullable types </li>    <li>Sequences with 