elements in the key and in the lock which prevent {HEAD ~ the lock} from changing from the locked condition to the unlocked condition when the key is not connected to the lock and which permit the lock to change from the locked condition to the unlocked condition when {TAIL ~ the key} is connected to the lock, 
elements in the key and in the lock which prevent { HEAD ~ the lock } from changing from the locked condition to the unlocked condition when the key is not connected to the lock and which permit the lock to change from the locked condition to the unlocked condition when { TAIL ~ the key } is connected to the lock ,
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH