a lid closing {HEAD ~ the outlet} of the outer chamber when the inner chamber is in {TAIL ~ the first position} 
a lid closing { HEAD ~ the outlet } of the outer chamber when the inner chamber is in { TAIL ~ the first position }
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL TAIL