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Professor Korner has generously supported school mathematics for more than 30 years and has been a good friend to NRICH since it started.
Some puzzles requiring no knowledge of knot theory, just a careful inspection of the patterns. A glimpse of the classification of knots, prime knots, crossing numbers and knot arithmetic.
What if the Earth's shape was a cube or a cone or a pyramid or a saddle ... See some curious worlds here.