Regrettably, there was a bug ¡­

Regrettably, there was a bug in the file parse.lsp that we provided as part of the current exercise. Our file actually contained part of the solution to part (4) of the exercise, viz. the recursive rules VP --> VP PP and NP --> NP PP. As some of you have discovered, rules of this type make our current parser go into an infinite loop. It is good to remember that C-c C-c (pressing the Control and C keys jointly, twice in a row) interrupts the Lisp system. To correct our mistake, either delete these rules from your current version, or retrieve a corrected version of our file