{TAIL ~ The coils} are switched in {HEAD ~ alternation} as a primary and a secondary coil 
{ TAIL ~ The coils } are switched in { HEAD ~ alternation } as a primary and a secondary coil
TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH