Left: The large rectangle is plastic and can be split into a square (blue) and two plastic rectangles (red and {green).
Centre: The two arcs drawn in each square.
Right: A Harriss spiral.
Image: Chalkdust.
More from Chalkdust
Christmas competition #3: ‘An eggnog mystery’
Lies, liquor and logical deduction play their part in this festive holiday tale
Top ten vote issue 07
Vote for your favourite unit
The mathematics of human migration
Human migration with mathematical models, data and a hands-on experiment!
In conversation with Marcus du Sautoy
We chat to Marcus about science communication, teaching mathematics in schools, and how to make group theory sound sexy.
In conversation with Bernard Silverman
We chat to the chief scientific advisor to the Home Office about the role of scientists and mathematicians in politics
Thoughts on the crossnumber
Did you use meta-logic to solve the crossnumber?