class Numeric
    def succ
      self + 1
    end
  end

  class Integer
    undef_method( :succ )
  end

  2.class  #=> Fixnum
  2.succ
  NoMethodError: undefined method `succ' for 1:Fixnum
          from (irb):10


Shouldn't it be able to find #succ in the ancestor?

T.