type(s) are always the correct ones to use.  For B-tree sort
      support functions, B-Tree equal image functions, and all
      functions in GiST, SP-GiST and GIN operator classes, it is
      necessary to specify the operand data type(s) the function is to
      be used with.
     </p><p>
      In a <code class="literal">DROP FUNCTION</code> clause, the operand data type(s) the
      function is intended to support must be specified.
     </p></dd><dt><span class="term"><em class="replaceable"><code>sort