KengoTODA
Programmer Passport: Prolog: potential errata (page 45)
At the end of page 45, there is a code snippet as follows:
path_with_length(a, f, [Path, Length]).
but this code brings Prolog into an error like below:
ERROR: Unknown procedure: path_with_length/3
ERROR: However, there are definitions for:
ERROR: path_with_length/4
false.
Probably we need to remove needless square brackets like below:
path_with_length(a, f, Path, Length).
Thanks for checking this post! 
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