Question 9
The Penrose Parlor ice-cream machine follows these rules:
0. Start with a cone.
1. Choose a flavour and add two scoops of that flavour.
2. Add one scoop of a different flavour on top.
3. Stop if the customer wants no more; otherwise repeat step 1.
Which pictured cone could not be made by the machine?
Editorial note: white shapes obscure the upper part of every original cone. The conditional comparison treats the visible scoops as bottom-up prefixes that may be completed above the obscured area; it cannot verify the complete hidden cones.
0. Start with a cone.
1. Choose a flavour and add two scoops of that flavour.
2. Add one scoop of a different flavour on top.
3. Stop if the customer wants no more; otherwise repeat step 1.
Which pictured cone could not be made by the machine?
Editorial note: white shapes obscure the upper part of every original cone. The conditional comparison treats the visible scoops as bottom-up prefixes that may be completed above the obscured area; it cannot verify the complete hidden cones.