match v1,v2 with
[],_ -> true
| _,[] -> false
- | s1::tl1, s2::_ when s1 < s2 -> sub_ex tl1 v2
- | s1::_, s2::_ when s2 < s1 -> false
- | s1::tl1, s2::tl2 -> (tl1,tl2)
+ | s1::_, s2::_ when s1 < s2 -> false
+ | s1::_, s2::tl2 when s2 < s1 -> sub_ex v1 tl2
+ | s1::tl1, s2::tl2 -> sub_ex tl1 tl2
;;