You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: keymap.rb
    path of file: ./repos/textbringer/lib/textbringer
    
    the code of the file until where you have to start completion: class Module
  def define_keymap(name)
    unless const_defined?(name, false)
      const_set(name, Textbringer::Keymap.new)
    end
  end
end

module Textbringer
  class Keymap
    include Enumerabl
    
    def lookup(key_sequence)
      case key_sequence.size
      when 0
        raise ArgumentError, "Empty key"
      when 1
        @map[key_sequence.first]
      else
        k, *ks = key_sequence
        km = @map[k]
        if km.is_a?(Keymap)
          km.lookup(ks)
        else
          nil
        end