includeの説明

include.rb

module M
  def hoge
    puts 'hoge'
  end
end

class C
  include M
end

a = C.new
a.hoge   # => hoge

include_ancestors.rb

module M
  def hoge
    puts 'hoge'
  end
end

class C
  include M
end

C.ancestors #=> => [C, M, Object, PP::ObjectMixin, Kernel, BasicObject]