a <em>predicate</em>, and returns another sequence. The output sequence is of the same element type (so if you put in a sequence of strings, you&#39;ll get a sequence of strings out) and it will only contain elements from the input sequence which pass the predicate. (Each item will be passed to the predicate in turn. If the predicate returns true, the item will be part of the output sequence; otherwise it won&#39;t.)</p>  <p>Now, a few important details about the behaviour:</p>  <ul>   <li>The input sequenc