module K
end

class O
  include K
end

class C < O
end

class D < O
end

module M
  def m
  end
end

module K
  include M
end

C.new.m # => undefined method
D.new.m # => undefined method

class D
  include K
end

D.new.m # => nil
C.new.m # => nil in Rubinius
# undefined method in MRI 1.8/1.9 and JRuby