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