Posing a goal

To get Prolog to do some computation, you need to issue a goal. Type

|?- grandmother(liz, Who).

Type this exactly, including the capital W and the final full-stop, and, hit <return>. Prolog will respond:¹

 Who = harry

Next, type a semi-colon followed by <return>. Prolog will respond

Who = wills

Again, type a semi-colon followed by <return>. Prolog will respond:

no

This means that you have now received all the responses to the goal that Prolog can compute on the basis of the information supplied in your program file.