Every vertex has an even degree, yet the picture cannot be drawn with a single stroke.
More from Chalkdust
Prize crossnumber, Issue 15
Win a £100 Maths Gear goody bag by solving our infamous puzzle
Top ten vote issue 15
Have your say
How to make: tessellating shortbread
Tasty and mathematical
Christmas conundrum #2
Solve this and you could be the lucky winner of a signed copy of The Indisputable Existence of Santa Claus
Advent quiz
Behind today's door... A quiz!
Advent facts I
Santa's sack of scientific surprises