Augment_specialised_args.Makeval rewrite_set_of_closures : 
  env:Inline_and_simplify_aux.Env.t ->
  duplicate_function:
    (env:Inline_and_simplify_aux.Env.t ->
      set_of_closures:Flambda.set_of_closures ->
      fun_var:Variable.t ->
      new_fun_var:Variable.t ->
      Flambda.function_declaration * Flambda.specialised_to Variable.Map.t) ->
  set_of_closures:Flambda.set_of_closures ->
  (Flambda.expr * Inlining_cost.Benefit.t) optionduplicate_function should be Inline_and_simplify.duplicate_function.