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