{HEAD ~ Its sole purpose} is to present some concepts in a simplified form as {TAIL ~ a prelude} to the more detailed description that is discussed later 
{ HEAD ~ Its sole purpose } is to present some concepts in a simplified form as { TAIL ~ a prelude } to the more detailed description that is discussed later
HEAD HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH