For the first exercise, can you refer to the on_route_to fact
which you were asked to write in the exercises on caves. You may have
found it too difficult to write, but you can appreciate what it means.
So what would its analogue mean in each of the three examples above?
Secondly, refer back to Lesson 2. In the three examples above, what are the analogues of (a) X being Y's parent; (b) X and Y being siblings; (b) X being Y's ancestor?