Reducing this to {HEAD ~ a common denominator} of 4:13 requires {TAIL ~ division} by a common divisor of 3 
Reducing this to { HEAD ~ a common denominator } of 4:13 requires { TAIL ~ division } by a common divisor of 3
OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH