sets.rb

# encoding: utf-8
require 'set'
require 'pp'

class Set
  def ∩(*args)
    intersection *args
  end

  def ∪(*args)
    union *args
  end

  def ⊂(*args)
    subset? *args
  end

  def ⊃(*args)
    superset? *args
  end
end

first = Set.new %w{a b c d}
second = Set.new %w{c d e f}
c = Set.new %w{c}

pp first.∩ second
pp first.∪ second
pp c.⊂ first
pp second.⊃ c