P_SINGLE_BOUNDARY
p->p_flag &= ~P_SINGLE_BOUNDARY;
p->p_flag |= P_SINGLE_BOUNDARY;
p->p_flag &= ~P_SINGLE_BOUNDARY;
(p->p_flag & P_SINGLE_BOUNDARY) && return_instead)
(p->p_flag & P_SINGLE_BOUNDARY) != 0,
p->p_flag &= ~(P_STOPPED_SINGLE | P_SINGLE_EXIT | P_SINGLE_BOUNDARY |