type t =
  | Var of string
  | Lam of string * t
  | App of t * t
  | Subst of string * t * t

module SSet : Set.S with type elt = string

val free_variables : t -> SSet.t
val free_variable_list : t -> string list
val pretty : t -> string
val push_subst : string -> t -> t -> t
val normalise : t -> t
val normalise_counted : t -> t * int * int
val to_named : t -> Named.t
val of_named : Named.t -> t
val alpha_equivalent : t -> t -> bool
val alpha_equivalent_susp : t -> t -> bool
val alpha_equivalent_counted : t -> t -> bool * int * int
val substitute : string -> t -> t -> t
val convert_from_named : Named.t -> t
val convert_to_named : t -> Named.t