# File lib/spruz/bijection.rb, line 3
    def self.[](*pairs)
      pairs.size % 2 == 0 or
        raise ArgumentError, "odd number of arguments for #{self}"
      new.fill do |obj|
        (pairs.size / 2).times do |i|
          j = 2 * i
          key = pairs[j]
          value = pairs[j + 1]
          obj.key?(key) and raise ArgumentError, "duplicate key #{key.inspect} for #{self}"
          obj.inverted.key?(value) and raise ArgumentError, "duplicate value #{value.inspect} for #{self}"
          obj[pairs[j]] = pairs[j + 1]
        end
      end
    end