 <code class="literal">OPR</code> is one of the operators listed in
     the index's <em class="firstterm">operator class</em>, another plan is created using
     the B-tree index to scan the relation. If there are further indexes
     present and the restrictions in the query happen to match a key of an
     index, further plans will be considered.  Index scan plans are also
     generated for indexes that have a sort ordering that can match the
     query's <code class="literal">ORDER BY</code> clause (if