anchor.diff:  let snapshot () = Common.snapshot push fstar_options ()
   let rollback depth = Common.rollback pop fstar_options depth
   
  -let set_option k v = Util.smap_add (peek()) k v
  +let set_option k v = Util.smap_add (internal_peek()) k v
   let set_option' (k,v) =  set_option k v
   
   let light_off_files : ref<list<string>> = Util.mk_ref []
  
positive.code: let _run = clear()
  
  let get_option s =
    match Util.smap_try_find (peek()) s with
    | None -> failwith ("Impossible: option " ^s^ " not found")
    | Some s -> s
  
  
negative.code: let fstar_options : ref<list<list<optionstate>>> = Util.mk_ref []
  
  let internal_peek () = List.hd (List.hd !fstar_options)
  let peek () = copy_optionstate (internal_peek())
  let pop  () = // already signal-atomic
      match !fstar_options with
      | []
  