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DonaldKellett/lpn-3-3p3.pl

Created December 22, 2018 05:30
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Learn Prolog Now! - Chapter 3 - Exercise 3.3 - Train routes
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lpn-3-3p3.pl
% Knowledge base of direct train routes (provided)
% Assumption: such direct train routes are unidirectional, i.e. directTrain(X, Y) does not imply directTrain(Y, X)
directTrain(saarbruecken,dudweiler).
directTrain(forbach,saarbruecken).
directTrain(freyming,forbach).
directTrain(stAvold,freyming).
directTrain(fahlquemont,stAvold).
directTrain(metz,fahlquemont).
directTrain(nancy,metz).
% travelFromTo/2 - can we travel from X to Y via a series of direct trains?
% We can travel from X to Y if there is a direct train from X to Y, or
% there is a direct train from X to some Z such that we can travel from Z to Y
travelFromTo(X, Y) :- directTrain(X, Y); directTrain(X, Z), travelFromTo(Z, Y).
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