Plang.Env
val create : unit -> t
val clear : t -> unit
val used : t -> string -> bool
val fresh : t -> sanitizer:( 'a -> string ) -> ?suggest:bool -> 'a -> string
val define : t -> string -> Lang.F.term -> unit
val unfold : t -> Lang.F.term -> unit
val set_indexed_vars : t -> unit
val iter : ( string -> Lang.F.term -> unit ) -> t -> unit