Solutions
wizard(harry).
scare(hagrid,dudley).
magical(X) :- wizard(X).
hate(uncle_vernon,X) :- magical(X).
hate(aunt_petunia,X) :- magical(X).
hate(aunt_petunia,X) :- scare(X,dudley).
This is, of course, not the only solution. What your knowledge base
looks like depends on the atoms that you choose to stand for
certain individuals and properties. The first fact could, for
example, also be encoded as
wizard('Harry').
or as
is_wizard(harry).