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