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