{HEAD ~ Bicycle drive unit} capable of {TAIL ~ backward movement} and naughtrotation and forward movement traveling when rectitude or reverse pedaling 
capable of
{ HEAD ~ Bicycle drive unit } capable of { TAIL ~ backward movement } and naughtrotation and forward movement traveling when rectitude or reverse pedaling
HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH