ruby alias_method for class methods

Generally, a ruby programmer could alias instance methods of a ruby object, but how could he alias class methods instead? The answer is he needs to understand how "self" works in ruby. If not yet knows, check out my presentation.

class Foo
  def a; 'a'; end
  alias_method :alias_for_a, :a

  def self.b; 'b'; end
  class <<self
    alias_method :alias_for_b, :b
  end
end

puts Foo.new.a
puts Foo.new.alias_for_a

puts Foo.b
puts Foo.alias_for_b