Your ping pong ball example sounds very much like the car in the garage problem which is explained well here: http://www.pitt.edu/~jdnorton/teaching/HPS_0410/ch

Your ping pong ball example sounds very much like the car in the garage problem which is explained well here: http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Reciprocity/index.html http://www.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/Rec... I suppose that's the same as the "ladder through the garage" paradox you mention?