theorem
  between5 a,b,c,d,e implies between a,b,c & between a,b,d &
  between a,b,e & between a,c,d & between a,c,e & between a,d,e &
  between b,c,d & between b,c,e & between b,d,e & between c,d,e &
  between4 a,b,c,d & between4 a,b,c,e & between4 a,c,d,e &
  between4 b,c,d,e;
