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Logic Programming School of Informatics, University of Edinburgh
append/3 A Drosophila of L.P.
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Logic Programming School of Informatics, University of Edinburgh
append/3 A Drosophila of L.P. As functions: append([], L) = L - - PowerPoint PPT Presentation
append/3 A Drosophila of L.P. As functions: append([], L) = L - - PowerPoint PPT Presentation
append/3 A Drosophila of L.P. As functions: append([], L) = L append([ H | T ], L) = [H | append(T, L) ] As a logic program append([], L, L) append([ H | T ], L, [ H | R ]) append(T, L, R) Logic Programming School of Informatics,
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Logic Programming School of Informatics, University of Edinburgh
Introduction to Negation as Failure
In Prolog the goal \+ G succeeds if no instance
- f G can be found by Prolog’s proof mechanism;
- therwise it fails.
p(X) :- q(X). q(1). q(2). r(2). s(3). Given: Goals: yes Results: \+ (p(1), r(1)). \+ (p(2), r(2)). \+ p(X). \+ (p(X), s(X)). no no yes
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Logic Programming School of Informatics, University of Edinburgh
Generating a Set of Results
setof(X, Goal, Set) generates the set, S, of instances of X generated by exhaustively satisfying the given Goal. Results: Goals: Given: S = [1,2] setof(X, p(X), S). setof(X, (p(X), r(X)), S). setof(X, (p(X) ; s(X)), S). setof(X, (p(X), s(X)), S). p(X) :- q(X). q(1). q(2). r(2). s(3). S = [2] S = [1,2,3] no
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Logic Programming School of Informatics, University of Edinburgh
Building Larger Definitions: Map Colouring The four colour theorem says that any 2- dimensional map can be coloured, with no bordering country sharing the same colour, using only four different colours.
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Logic Programming School of Informatics, University of Edinburgh
A Logic Program Requirement
Define a predicate colour_countries(X) that generates in X a list of terms [c(S,C),…], where S is a country and C is one of four
- colours. The predicate must be able to generate each
combination of countries and colours satisfying the four-colour theorem but no combinations that do not satisfy the theorem. An example behaviour is: | ?- colour_countries(X). X=[c(austria,red), c(belgium,green), c(denmark,yellow), c(france,red), c(germany,blue), c(italy,blue), c(netherlands,yellow), c(portugal,blue), c(spain,yellow), c(switzerland,yellow)]
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Logic Programming School of Informatics, University of Edinburgh
A Representation of a Map
ngb(portugal, [spain]). ngb(spain, [portugal,france]). ngb(france, [spain,belgium,switzerland,germany,italy]). ngb(belgium, [france,germany,netherlands]). ngb(netherlands, [belgium,germany]). ngb(germany, [netherlands,belgium,france,switzerland,austria,denmark]). ngb(switzerland, [france,germany,austria,italy]). ngb(austria, [germany,switzerland,italy]). ngb(italy, [france,switzerland,austria]). ngb(denmark, [germany]).
Note this is not the only representation we could have used. The art is to describe the salient and essential details of the problem, and no more than this.
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Logic Programming School of Informatics, University of Edinburgh
Generating Individual Neighbours
neighbour(Country, Country1) :- ngb(Country, Neighbours), member(Country1, Neighbours). member(X, [ X | _ ]). member(X, [ _ | T ]):- member(X, T).
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Logic Programming School of Informatics, University of Edinburgh