For example, frames specify {HEAD ~ operations} to be performed on {TAIL ~ internal entities} such as variables or timers, for example 
to be performed on
For example , frames specify { HEAD ~ operations } to be performed on { TAIL ~ internal entities } such as variables or timers , for example
OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH