n the queries that
   are supposed to benefit from the index.  To be precise, a partial
   index can be used in a query only if the system can recognize that
   the <code class="literal">WHERE</code> condition of the query mathematically implies
   the predicate of the index.
   <span class="productname">PostgreSQL</span> does not have a sophisticated
   theorem prover that can recognize mathematically equivalent
   expressions that are written in different forms.  (Not
   only is such a general theorem pro