Every vertex has an even degree, yet the picture cannot be drawn with a single stroke.
More from Chalkdust
A Year in Numbers
We review the seventh of this year's nominees for Book of the Year
Dear Dirichlet, Issue 14
Football, telly and shape-shifting houses find their way into the prof's postbox this issue.
The croissant equation
Each time you eat a croissant you might be biting more than 500 layers of dough!
Origami tesseract
Folding origami, building networks, making projections and multiple dimensions!
Dear Dirichlet, Issue 02
Moonlighting agony uncle Professor Dirichlet answers your personal problems.
Newsletter puzzles
These puzzles appeared in the Chalkdust newsletters. You can find the answers here and sign up for the newsletter here.