Anyone interested in learning postscript should also consider Glenn Reid's Thinking in PostScript. I think it is a better introduction than the blue book.
Reid is also listed on the title page as the author of the green book.
Glenn Reid's Green Book is to PostScript as Leo Brodie's Thinking Forth is to FORTH! Both classic excellent books on how to think like a native in the language.
Reid is also listed on the title page as the author of the green book.