1 files changed, 50 insertions, 0 deletions
diff --git a/sem7/pp/prolog/lec4.pl b/sem7/pp/prolog/lec4.pl
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+++ b/sem7/pp/prolog/lec4.pl
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+
+last([X], X).
+last([_|XS], X) :- last(XS, X).
+
+/*
+last([1,2,3], X) # Bruger regel 2
+last([2,3], Y) # Bruger regel 2
+last([3], Z) # Bruger regel 1, så Z = 3
+# Så Y = Z = 3
+# Så X = Y = Z = 3
+
+
+Okay det er også bare fint at skrive
+last([1,2,3],X)
+     |
+last([2,3],X)
+     |
+last([3], X)
+*/
+
+attach([], E, [E]).
+attach([X|XS], E, [X|R]) :- attach(XS, E, R).
+
+
+/*
+Proof search of attach
+
+attach([1,2], a, L)
+        |      X = 1, XS = [2], E = a, L = [1|L1]
+attach([2], a, L1)
+        |      X1 = 2, XS1 = [], E1 = a, L1 = [2|L2]
+attach([], a, L2)
+        |      E2 = a, L2 = [a]
+*/
+
+nat(zero).
+nat(succ(X)) :- nat(X).
+
+after(succ(X), X).
+
+leq(zero, Y) :- nat(Y).
+leq(succ(X), succ(Y)) :- leq(X, Y), nat(X), nat(Y).
+
+add(X, zero, X) :- nat(X).
+add(X, succ(Y), succ(R)) :- add(X, Y, R), nat(X), nat(Y), nat(R).
+
+sub(X, Y, R) :- add(R, Y, X).
+
+min(X, Y, X) :- leq(X, Y).
+min(succ(X), Y, Y) :- leq(Y, X).