If at least one check node is unsatisfied, {HEAD ~ the decoder} reports {TAIL ~ a failure} 
reports
If at least one check node is unsatisfied , { HEAD ~ the decoder } reports { TAIL ~ a failure }
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL