29. Jigsaw Puzzle. Everyone is familiar with the puzzle that involves cutting a piece of plywood with a picture drawn on it into small pieces, and then proposing to reassemble the original picture from these mixed pieces. Let the picture be cut into $n$ small pieces. We will call a "move" the joining together of two pieces, regardless of whether each piece consists of one or several small pieces previously joined. How should one act to assemble the picture in the minimum number of moves $?^{*}$[^1]
29. Since we start with $n$ pieces and end up with 1, and since each move reduces the number of pieces by 1, the puzzle can be assembled in $n-1$ moves, and this number clearly does not depend on the method of joining. Of course, this reasoning remains valid only under the condition that, once any parts are joined together, they are not separated again.

[Leo Moser, M. M., 26, 169 (January 1953).]