# File lib/ruote/util/subprocess.rb, line 70
  def self.is_tree?(arg)

    arg.is_a?(Array) && arg.size == 3 &&
    arg[0].is_a?(String) && arg[1].is_a?(Hash) && arg[2].is_a?(Array) &&
    (arg.last.empty? || arg.last.find { |e| ! is_tree?(e) }.nil?)
  end