Definition bneq_empty_string(s:string):bool :=
match (string_dec s ""%string) with
| left _ => false
| right _ => true
end.(** ** Lemmas for list *)

Definition concat_list_string(xs:list string) := 
  fold_right (fun s s' : string => (s ++ s')%string) ""%string xs.

Lemma concat_list_string_xs_x : forall (xs:list string)(x:string), concat_list_string (xs ++ x::nil) = ((concat_list_string xs) ++ x)%string.