module rec A : sig
  class virtual c:
    object
      method a: string;
    end;
end = struct
  class virtual c =
    object
      method  a = "a";
    end;
end
and B : sig
  class c:
    object
      inherit A.c;
      method b:string;
    end;
end = struct
  class c =
    object
      inherit A.c;
      method b = "b";
    end;
end
and C : sig
  class c:
    object
      inherit B.c;
      method c: string;
    end;
end = struct
  class c =
    object
      inherit B.c;
      method c = "c";
    end;
end;