target = 17
  set = [6.0,6.0,5.0,2.0]
  set.permutation(4).each { |s|
    [:+,:-,:*,:/].repeated_permutation(3).each{ |e|
      p s.zip(e).flatten.compact.join(' ') if ->(){o=s[0];(0..2).each{|i|o=o.send(e[i],s[i+1])};o}.call==t
      p ['(', '','',')','(','','',')'].zip(s.zip(e).flatten).join(" ") if eval(['(', '','',')','(','','',')'].zip(s.zip(e).flatten).join(" ")) == t
    }
  }