normalize vector product

#!/usr/bin/env ruby
module NormalVector
  refine Array do
    def normal(o)
      require 'matrix'
      Vector.elements(self.map &:to_f)
      .cross(Vector.elements(o))
      .normalize.to_a
    end
  end
end
using NormalVector
puts "#{[1, 2, 3].normal [4, 5, 6]}"