# File lib/ruote/part/engine_participant.rb, line 149
    def cancel(fei, flavour)

      exps = @storage.get_many('expressions', /^0![^!]+!#{fei.wfid}$/)

      return true if exps.size < 1
        # participant expression will reply to its parent

      @storage.put_msg(
        'cancel',
        'fei' => exps.first['fei'],
        'flavour' => flavour)

      false
        # participant expression will NOT reply to its parent
    end