In one of his wonderful books on recreational mathematics, Martin Gardner comments that, just as trains, planes, ships, automobiles and other means of transportation appear in numerous problems, it would seem that elevators have been forgotten by lovers of logical puzzles. . This does not seem to be the case with my sagacious readers, who continue to ponder a problem raised several weeks ago in the delivery Problematic elevators. The problem in question is the following, and in addition to finding the smallest number of elevators, the situation lends itself to raising other interesting questions (see comments from last week):
