Stone shadows: stack stones until three shadows agree
Three lanterns cast one plot of stones onto three walls. The walls are drawn; the stones are not. Stand stones on the plot until every wall agrees. The front wall cannot tell how far back a stone stands, and the side wall cannot tell which column it is in — only all three together pin it down.
1 short
From the front: column 1 no, column 2 one, column 3 no, column 4 no. 1 short.
1 short
From the side: row 1 no, row 2 one, row 3 no, row 4 no. 1 short.
1 short
From above: stones on row 2 column 2. 1 short.
None of the three shadows agrees yet.