$ ruby example_address_book.rb
[#<Group:0xddf24 @desc="my family", @name="family">,
 #<Group:0xddf10 @desc="my friends", @name="friend">,
 #<Group:0xdde84 @desc="those who works together", @name="business">]
[#<Person:0xdefdc
  @birth=#<Date: 4903089/2,0,2299161>,
  @blood="A",
  @deleted=false,
  @desc=nil,
  @email=nil,
  @group="family",
  @name="Sumire",
  @phone=nil>,
 #<Person:0xdee9c
  @birth=#<Date: 4899437/2,0,2299161>,
  @blood=nil,
  @deleted=false,
  @desc=nil,
  @email="shiina@mail.org",
  @group="friend",
  @name="Shiina",
  @phone=nil>,
 #<Person:0xde8e8
  @birth=nil,
  @blood=nil,
  @deleted=false,
  @desc=nil,
  @email="cherry@mail.net",
  @group="business",
  @name="Sakura",
  @phone="012-345-6789">]
