gzip is the file compressor program of the GNU project. gzip now has its own home page: http://www.gzip.org/. gzip is free, available for most computers and operating systems, and very good (actually better than most other similar programs). If you do not have it, complain with your computer administrator or download it. It is also possible that gzip is in your system, but not on your path: its usual locations are /usr/local/bin/gzip or /bin/gzip. If you have it in your system but are not familiar with it here is a minimal explanation of what you have to do (at least in a UNIX system). Assuming you downloaded a file called bobo.ps.gz, type gunzip bobo.ps.gz: this should recreate the original file bobo.ps. You may read the man page for gzip here. The Windows program winzip is also capable of decompressing *.gz files but if you use Windows you may want to install software from GNU-Win.