{HEAD ~ a thyristor free wheeling diode} connected in {TAIL ~ antiparallel relationship} with the respective thyristor 
{ HEAD ~ a thyristor free wheeling diode } connected in { TAIL ~ antiparallel relationship } with the respective thyristor
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH