text: #!/usr/bin/env python
  
  from threading import Timer
  
  import rospy
  from geometry_msgs.msg import Twist, Pose2D, PoseStamped
  from std_msgs.msg import *
  from move_base_msgs.msg import *
  from actionlib_msgs.msg import *
  from apriltags_ros.msg import *
  
  avalability = False
  tagOne = False
  tagTwo = False
  checkCBPub = rospy.Publisher('/checkEVcb',Bool,queue_size=1)
  
  def detectionCB(tagArray):
      global tagOne, tagTwo
      if len(tagArray.detections) != 0:
          for tag in tagArray.detections:
              if tag.id == 1:
                  tagOne = True
                  print 'tag one OK'
              elif tag.id == 2:
                  tagTwo= True
                  print 'tag two OK'
              else:
                  pass
      else:
          return
      return
  
  def chekc_elevator(msg):
      global tagOne, tagTwo
      tagOne = False
      tagTwo = False
      t = Timer(3,chekc_elevatorCB)
      t.daemon = True
      t.start()
      return
  
  def chekc_elevatorCB():
      global tagOne, tagTwo, checkCBPub
      print str(tagOne),str(tagTwo)
      if tagOne and tagTwo:
          checkCBPub.publish(True)
      else:
          checkCBPub.publish(False)
      return    
  
  
  
  
  if __name__=="__main__":
      rospy.init_node('elevator_checker')
      rospy.Subscriber('/camera_rear/tag_detections',AprilTagDetectionArray,detectionCB)
      rospy.Subscriber('/checkEV',Bool,chekc_elevator)
  
      rospy.spin()