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
A Year in Numbers
We review the seventh of this year's nominees for Book of the Year
Dear Dirichlet, Issue 18
Phone assistants, duplicating pastries, and being a 10 anywhere else are among the topics of discussion in this issue's Dear Dirichlet advice column
The magic of particle prediction
Madi Hammond shows us how physicists are predicting the fundamental particles of the universe.
Christmas competition #3: ‘An eggnog mystery’
Lies, liquor and logical deduction play their part in this festive holiday tale
New largest prime number discovered!
Amaze your friends with our top facts about the new largest known prime number
Roots: All things being equal
The story of how we got the equals sign