Data Structure Use this category if you need help with a specific data structure or trying to find a data structure, e.g. Association lists or Ordered Sets PlDoc When you need help with PlDoc (SWI-Prolog documentation), e.g. writing declaration headers, creating output, etc. Algorithm Use this category when you need help implementing an algorithm. If you need help with a single predicate then use the Help - Predicate category instead. Tools Use when needing help with tools such as Emacs as opposed to needing help with coding. Pack Use this when you need help with a Pack. Predicate When you are not sure which SWI-Prolog base or library predicate, combination of predicates, or options for a predicate(s) to use.