like18.c

	else if (IsA(rawreq, SupportRequestIndexCondition))
	{
		/* Try to convert operator/function call to index conditions */
		SupportRequestIndexCondition *req = (SupportRequestIndexCondition *) rawreq;

		/*
		 * Currently we have no "reverse" match operators with the pattern on
		 * the left, so we only need consider cases with the indexkey on the
		 * left.
		 */
		if (req->indexarg != 0)
			return NULL;

		if (is_opclause(req->node))
		{
			OpExpr	   *clause = (OpExpr *) req->node;

			Assert(list_length(clause->args) == 2);
			ret = (Node *)
				match_pattern_prefix((Node *) linitial(clause->args),
									 (Node *) lsecond(clause->args),
									 ptype,
									 clause->inputcollid,
									 req->opfamily,
									 req->indexcollation);
		}
		else if (is_funcclause(req->node))	/* be paranoid */
		{
			FuncExpr   *clause = (FuncExpr *) req->node;

			Assert(list_length(clause->args) == 2);
			ret = (Node *)
				match_pattern_prefix((Node *) linitial(clause->args),
									 (Node *) lsecond(clause->args),
									 ptype,
									 clause->inputcollid,
									 req->opfamily,
									 req->indexcollation);
		}
	}

	return ret;
}