gistfile1.rb

irb(main):048:0> module P
irb(main):049:1> def a; puts 'a'; end
irb(main):050:1> module_function :a
irb(main):051:1> end
=> P
irb(main):052:0> P.a
a
=> nil
irb(main):053:0> P::a
a
=> nil
irb(main):054:0> class E
irb(main):055:1> include P
irb(main):056:1> end
=> E
irb(main):057:0> E.a
NoMethodError: undefined method `a' for E:Class
	from (irb):57
	from /Users/ka8725/.rbenv/versions/1.9.2-p290/bin/irb:12:in `<main>'
irb(main):058:0> E.new.a
NoMethodError: private method `a' called for #<E:0x007fe06d16cf38>
	from (irb):58
	from /Users/ka8725/.rbenv/versions/1.9.2-p290/bin/irb:12:in `<main>'
irb(main):059:0> module Q
irb(main):060:1> def a; puts a; end
irb(main):061:1> end
=> nil
irb(main):062:0> class E
irb(main):063:1> include Q
irb(main):064:1> end
=> E
irb(main):065:0> E.a
NoMethodError: undefined method `a' for E:Class
	from (irb):65
	from /Users/ka8725/.rbenv/versions/1.9.2-p290/bin/irb:12:in `<main>'
irb(main):066:0> E.new.a
SystemStackError: stack level too deep
	from /Users/ka8725/.rbenv/versions/1.9.2-p290/lib/ruby/1.9.1/irb/workspace.rb:80
Maybe IRB bug!!
irb(main):067:0> E.ancestors
=> [E, Q, P, Object, Kernel, BasicObject]