fact: Definition Level_20 := |> _ _ _ _ _ # # # # <| |> _ _ _ _ _ # _ _ # <| |> # # # # # # X O # <| |> # _ _ _ X _ X O # <| +> # _ X + X O O O # <| |> # _ X X X O O # # <| |> # _ _ X _ O O # <| |> # # # # # # # # <| |><| .