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gistfile1.rb

class Tree
  include Comparable

  attr_accessor :age

  def initialize(age)
    @age = age
  end

  def <=> another_tree
    age <=> another_tree.age
  end
end

t1 = Tree.new(3)
t2 = Tree.new(3) 
t3 = Tree.new(4)

puts t1 == t2 #true
puts t1 == t3 #false