My gps-equipped radiowave controllable robot Lori is somewhere on the surface of Earth. I order her to drive 100 miles South and she obeys. Then I order her to drive 100 miles West and she obeys. Then I order her to drive 100 miles North and she obeys. After this I look at my gps receiver and notice that Lori is exactly where she was at the beginning of the story.

Classify all points where she could have started given this knowledge

2/5

The north pole, and all points 100 miles north of the southernmost 100-mile length latitude line.

Good start. But that’s not all points yet. :)

Also all the points of the southernmost 100-mile length latitude line and the south pole, I guess..

Very nice blog, by the way..

I was wrong, not the pole.

Yes, the robot couldn’t have obeyed me if she were on the South pole and I ordered her to go South… hint: there are infinitely many more solutions similar to Rick Woods’ partial solution.

And thanks!

Next attempt: the north pole, and all points 100 miles north of all the southernmost 100-mile/n length latitude lines, for n=1,2,3…

Kari K’s solution is the same as mine.