Add practical no. 1 and 2 from chapter 3.

lpn/ch03/connected.pl

@@ -0,0 +1,60 @@
+%% Imagine that the following knowledge base describes a maze. The
+%% facts determine which points are connected, that is, from which
+%% points you can get to which other points in one step. Furthermore,
+%% imagine that all paths are one-way streets, so that you can only
+%% walk them in one direction. So, you can get from point 1 to point
+%% 2, but not the other way round.
+connected(1,2).
+connected(3,4).
+connected(5,6).
+connected(7,8).
+connected(9,10).
+connected(12,13).
+connected(13,14).
+connected(15,16).
+connected(17,18).
+connected(19,20).
+connected(4,1).
+connected(6,3).
+connected(4,7).
+connected(6,11).
+connected(14,9).
+connected(11,15).
+connected(16,12).
+connected(14,17).
+connected(16,19).
+
+
+%% Write a predicate path/2 that tells you from which points in the
+%% maze you can get to which other points when chaining together
+%% connections given in the above knowledge base. Can you get from
+%% point 5 to point 10? Which other point can you get to when starting
+%% at point 1? And which points can be reached from point 13?
+
+path(X, Y) :- connected(X, Y).
+path(X, Y) :- connected(X, Z),
+	      path(Z, Y).
+
+%% Questions:
+%% 1. Can you get from point 5 to point 10? Yes:
+%%
+%%     ?- path(5, 10).
+%%     true .
+%%
+%% 2. Which other point can you get when starting at point 1? You can't
+%%    get to any other points:
+%%
+%%     ?- path(1, P).
+%%     P = 2 ;
+%%     false.
+%%
+%% 3. Which points can be reached from point 13? Points 9, 10, 14, 17,
+%%    18.
+%%
+%%     ?- path(13, P).
+%%     P = 14 ;
+%%     P = 9 ;
+%%     P = 17 ;
+%%     P = 10 ;
+%%     P = 18 ;
+%%     false.

lpn/ch03/travel.pl

@@ -11,3 +11,49 @@ directTrain(nancy,metz).
 travelFromTo(X, Y) :- directTrain(X, Y).
 travelFromTo(X, Y) :- directTrain(X, Z),
                       travelFromTo(Z, Y).
+
+%% New version from practical exercises.
+%% We are given the following knowledge base of travel information:
+byCar(auckland,hamilton).
+byCar(hamilton,raglan).
+byCar(valmont,saarbruecken).
+byCar(valmont,metz).
+
+byTrain(metz,frankfurt).
+byTrain(saarbruecken,frankfurt).
+byTrain(metz,paris).
+byTrain(saarbruecken,paris).
+
+byPlane(frankfurt,bangkok).
+byPlane(frankfurt,singapore).
+byPlane(paris,losAngeles).
+byPlane(bangkok,auckland).
+byPlane(singapore,auckland).
+byPlane(losAngeles,auckland).
+
+%% Write a predicate travel/2 which determines whether it is possible
+%% to travel from one place to another by chaining together car,
+%% train, and plane journeys. For example, your program should answer
+%% yes to the query travel(valmont,raglan).
+
+%% The base case is a direct route via car, train or plane.
+travelDirect(X, Y) :- byCar(X, Y).
+travelDirect(X, Y) :- byTrain(X, Y).
+travelDirect(X, Y) :- byPlane(X, Y).
+travel(X, Y)       :- travelDirect(X, Y).
+
+%% The recursive case chains these together.
+travel(X, Y) :- travel(X, Z),
+		travel(Z, Y).
+
+%% So, by using travel/2 to query the above database, you can find out
+%% that it is possible to go from Valmont to Raglan. If you are
+%% planning such a voyage, that’s already something useful to know,
+%% but you would probably prefer to have the precise route from
+%% Valmont to Raglan. Write a predicate travel/3 which tells you which
+%% route to take when travelling from one place to another. For
+%% example, the program should respond
+%% X  =  go(valmont,metz,
+%%  	      go(metz,paris,
+%%  		    go(paris,losAngeles)))
+%% to the query travel(valmont,losAngeles,X).