solution.rb

require "active_support"

module M1
  def m; 1 end
end

module M2
  def m; super + 1 end
end

# monkey patch M1 and M2 to inc m + 1
module P
  extend ActiveSupport::Concern
  included do
    alias_method_chain :m, :patch
  end
  def m_with_patch
    m_without_patch + 1
  end
end
M1.send :include, P
M2.send :include, P
# end mp

class C1
  include M1
end

class C2
  include M1
  include M2
end

puts C1.new.m # must be > 1
puts C2.new.m # must be > 2