Alternatively {HEAD ~ L1} and D2 may be functionally viewed as {TAIL ~ a smoothing filter} with an input at terminal 15 
functionally viewed as
Alternatively { HEAD ~ L1 } and D2 may be functionally viewed as { TAIL ~ a smoothing filter } with an input at terminal 15
OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH