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Exercise 4.1
How does Prolog respond to the following queries?
[a,b,c,d] = [a,[b,c,d]].
[a,b,c,d] = [a|[b,c,d]].
[a,b,c,d] = [a,b,[c,d]].
[a,b,c,d] = [a,b|[c,d]].
[a,b,c,d] = [a,b,c,[d]].
[a,b,c,d] = [a,b,c|[d]].
[a,b,c,d] = [a,b,c,d,[]].
[a,b,c,d] = [a,b,c,d|[]].
[] = _.
[] = [_].
[] = [_|[]].
Exercise 4.2
Suppose we are given a knowledge base with the following facts:
tran(eins,one).
tran(zwei,two).
tran(drei,three).
tran(vier,four).
tran(fuenf,five).
tran(sechs,six).
tran(sieben,seven).
tran(acht,eight).
tran(neun,nine).Write a predicate
listtran(G,E)
which translates a list of German number words to the corresponding list of English number words. For example:listtran([eins,neun,zwei],X).
should give:
X = [one,nine,two].
Your program should also work in the other direction. For example, if you give it the query
listtran(X,[one,seven,six,two]).
it should return:
X = [eins,sieben,sechs,zwei].
Hint: to answer this question, first ask yourself `How do I translate the empty list of number words?'. That's the base case. For non-empty lists, first translate the head of the list, then use recursion to translate the tail.
Exercise 4.3
Write a predicate
twice(In,Out)
whose left argument is a list, and whose right argument is a list consisting of every element in the left list written twice. For example, the querytwice([a,4,buggle],X).
should return
X = [a,a,4,4,buggle,buggle]).
And the query
twice([1,2,1,1],X).
should return
X = [1,1,2,2,1,1,1,1].
Hint: to answer this question, first ask yourself `What should happen when the first argument is the empty list?'. That's the base case. For non-empty lists, think about what you should do with the head, and use recursion to handle the tail.
Exercise 4.4
Draw the search trees for the following three queries:
?- member(a,[c,b,a,y]).
?- member(x,[a,b,c]).
?- member(X,[a,b,c]).
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