{HEAD ~ The fixed nonlinear function processing units} in {TAIL ~ a given stage} implement only the nonlinear function needed for the MD5 round being performed by the stage 
in
{ HEAD ~ The fixed nonlinear function processing units } in { TAIL ~ a given stage } implement only the nonlinear function needed for the MD5 round being performed by the stage
HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH