If {HEAD ~ the file} is not present on {TAIL ~ the client} or if the command would fail, the present invention ignores the command and does not attempt to execute it later 
is not present on
If { HEAD ~ the file } is not present on { TAIL ~ the client } or if the command would fail , the present invention ignores the command and does not attempt to execute it later
OTH HEAD HEAD HEAD HEAD HEAD HEAD REL REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH