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 In_list_append_left : forall A (a:A) l l', In a l -> In a (l ++ l')%list.