def check_arity(obj, n_args)
    ary = obj.arity

    if ary >= 0
      n_args == ary
    else
      n_args >= (ary+1).abs
    end
  end
def check_arity(obj, n_args)
    ary = obj.arity

    if ary >= 0
      n_args == ary
    else
      n_args >= (ary+1).abs
    end
  end
returns true, if the arity of "obj" matches