Module#prepend - using include on 1.9.x

prepend.rb

class C
   def x; "x"; end
end

module M
   def x; '[' + super + ']'; end
   def y; "y"; end
end

class C
   include M
end

p C.ancestors # [C, M, Object, Kernel, BasicObject]
c = C.new
puts c.x # => x 
puts c.y # => y