In {HEAD ~ the preferred embodiments} {TAIL ~ two reciprocating members} are provided and arranged so that one is in its lower position when the other is in the upper position 
In { HEAD ~ the preferred embodiments } { TAIL ~ two reciprocating members } are provided and arranged so that one is in its lower position when the other is in the upper position
OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH