module type Univariate_polynomial_sig = sig
  type 'coeff t

  (*  include Ring with type 'coeff t := 'coeff t *)

  val create : ('coeff * int) list -> 'coeff t
  val degree : 'coeff t -> Signed.Long.t
  val get_coeff : 'coeff t -> int -> 'coeff
  val eval : 'coeff t -> 'coeff -> 'coeff
  val deriv : ?indeterminate:int -> _ t -> _ t
  val derivn : ?indeterminate:int -> _ t -> int -> _ t

  val fft :
    (module Finite_cyclic_group_sig with type t = 'coeff) ->
    'coeff t ->
    'coeff t Arrays.t
end

val univariate_polynomial : (module Ring with type t = 't) ->
  (module Univariate_polynomial_sig with type 'coeff t  constraint 'coeff= 't)
the last line doesn't typecheck: invalid package type: only 'with type t =' constraints are supported