A locked state managed by {HEAD ~ the blocker} greatly reduces corner cases and simplifies {TAIL ~ solutions} in the few remaining corner cases 
A locked state managed by { HEAD ~ the blocker } greatly reduces corner cases and simplifies { TAIL ~ solutions } in the few remaining corner cases
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH