public static boolean subrelationRuleP(Proposition rule) {
    return ((rule.kind == GuiServer.KWD_IMPLIES) &&
        (Stella_Object.isaP((rule.arguments.theArray)[0], GuiServer.SGT_LOGIC_NAMED_DESCRIPTION) &&
         Stella_Object.isaP((rule.arguments.theArray)[1], GuiServer.SGT_LOGIC_NAMED_DESCRIPTION)));
  }