{HEAD ~ A propulsor system} is {TAIL ~ an assembly} of individual propulsors that act in concert to form a substantially continuous control surface that undulates in a working fluid 
is
{ HEAD ~ A propulsor system } is { TAIL ~ an assembly } of individual propulsors that act in concert to form a substantially continuous control surface that undulates in a working fluid
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL 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