LINKFOR
PARENT(tp) = LEFT(tp) = RIGHT(tp) = LINKFOR(tp) = NULL;
LINKFOR(tp) = np;
if ((sp = LINKFOR(op)) != NULL)
LINKFOR(tp) = sp;
if ((tp = LINKFOR(op)) != NULL) {
PARENT(tp) = LEFT(tp) = RIGHT(tp) = LINKFOR(tp) = NULL;
LINKFOR(tp) = np;
if ((sp = LINKFOR(op)) != NULL) {
LINKFOR(tp) = sp;
if ((tp = LINKFOR(op)) != NULL) {