TCursorBack()
TCursorBack(void)
TCursorBack(){	register TScreen *screen = &term->screen;	register struct Tek_Char *t;	register int x, l;	x = ( screen->cur_X -=		(t = &TekChar[screen->cur.fontsize])->hsize	    );	if(((screen->margin == MARGIN1) && (x < 0))	|| ((screen->margin == MARGIN2) && (x < TEKWIDTH / 2))) {		if((l = (screen->cur_Y + (t->vsize - 1)) / t->vsize + 1) >=		 t->nlines) {			screen->margin = !screen->margin;			l = 0;		}		screen->cur_Y = l * t->vsize;		screen->cur_X = (t->charsperline - 1) * t->hsize;	}}