{HEAD ~ The tub} thus has {TAIL ~ sidewalls} defining arm rests, end walls defining a foot rest and back rest, and a bottom defining a seat 
has
{ HEAD ~ The tub } thus has { TAIL ~ sidewalls } defining arm rests , end walls defining a foot rest and back rest , and a bottom defining a seat
HEAD HEAD HEAD HEAD HEAD HEAD OTH REL 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