ISTTYOPEN
if (!ISTTYOPEN(tp)) {
if (ISTTYOPEN(tp)) {
&& ISTTYOPEN(tp)
if (!ISTTYOPEN(tp)) {
if (ISTTYOPEN(tp))
if (ISTTYOPEN(tp)) {
if (ISTTYOPEN(tp)) {
if (!ISTTYOPEN(tp)) {
if (!ISTTYOPEN(tp)) {
if (!ISTTYOPEN(cur_tty)) {
if (!ISTTYOPEN(cur_tty))