{HEAD ~ Piston machine}, which operates either as an engine or as {TAIL ~ a working machine}, the piston machine comprising: 
{ HEAD ~ Piston machine } , which operates either as an engine or as { TAIL ~ a working machine } , the piston machine comprising :
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL OTH OTH OTH OTH OTH REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH