# Prolog Homework for Practice – Prolog Problems

1) Perform suitable substitutions of variables (by ‘people’) and then use resolution to prove from { ¬ parent(Y,X), child(X,Y) }, { gchild(X,Z), ¬ child(X,Y), ¬ child(Y,Z) }, and selected basic facts from the original family.pl program ( { parent(pat, jim) }, etc.) the goal G which says that tom has a gchild [ child(X,Y) means X is a child of Y and gchild(X,Y) means that X is a grandchild of Y ]. Of course, this means that you have to (resolution) refute ¬ G. That is, answer i), do ii) and answer iii).

i) What is G, what is ¬ G?
ii) Prove G, that is, give a resolution refutation (a tree proof of □ ) from ¬G plus selected
clauses (indicate the required substitutions).
iii) Which clauses do you need to get □? Do you have a choice?

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2) Abstract resolution with predicates and variables: Construct a resolution tree proof of the empty clause □ from the given set of clauses. Clearly indicate which clauses you used, the literal resolved on, and the substitutions made at each step. Do you need all clauses? Capital letters X,Y,U,V,W indicate variables, but a, b, c are constants (as in Prolog). Hint: This is easier than it looks at first.
1) { P(a, X, f(Y)), P(a, Z, f(h(b))), ¬Q(Y, Z) }
2) { ¬Q(h(b), W), H(W, a) }
3) { ¬P(a, W, f(h(b))), H(X,a) }
4) { P(a, c, f(h(U))), H(U,a), Q(h(b), b) }
5) { ¬H(V,a) }

3) More monkey business… (cf. 06_Monkey_A_2023_m.pl)
a) Write a cangetwn/2 predicate that performs a countdown, thus limiting the number of moves the monkey can make. Here is a suggestion how it might look like (N, the number of moves the monkey may still do, is given by the user):
cangetwn( state( ,,_,has ),N ) :- writeln([‘got it!!’, N]).
cangetwn(S1,N):- /If N is positive, subtract 1 to get M for next move/
move( S1,Move,S2 ),writeln([M,move(S1,Move,S2)]),
cangetwn(/What goes here?/).
b) Can this be used to make Prolog find aerobic paths to the banana with some unclimbing?
c) How many moves are ‘used’ by cangetwn when unclimbs are allowed?
d) How does this compare to the situation when unclimbs are not allowed?
e) Is it (with this cangetwn) possible to allow all three suggested unclimbings at once?