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