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 forallb_list_xs_x : forall A (f:A -> bool)(xs:list A)(x:A), forallb f xs = true -> f x = true -> forallb f (xs ++ x::nil)%list = true.