India, April 21 -- Suppose you walk up a escalator that is itself moving up. Do you count more steps or fewer compared to moving up a stationary staircase of the same length? What happens if you walk down while the escalator moves up, or vice versa? How does the number of steps you walk change as you vary your walking speed, or the number of steps you cover with each stride?

Puzzles with escalator steps offer a number of variations. As far as I can remember, they have been used only once in Problematics, and that was in the early days of this column in its current form in HT, close to two-and-a-half years ago. So here's a selection for you, picked up from various published sources and adapted to Problematics-like situations.

#Puzzle 139...