tributes that are not simple column
       references.  This is a list with one element for each zero
       entry in <TT
CLASS="STRUCTFIELD"
>indkey</TT
>.  Null if all index attributes
       are simple references.
      </TD
></TR
><TR
><TD
><TT
CLASS="STRUCTFIELD"
>indpred</TT
></TD
><TD
><TT
CLASS="TYPE"
>pg_node_tree</TT
></TD
><TD
>&nbsp;</TD
><TD
>       Expression tree (in <CODE
CLASS="FUNCTION"
>nodeToString()</CODE
>
       representation) for partial index predicate.  Null if not a
       partia