In the first paragraph on page 143, I made the assertionAlthough triangular stamps have come in a variety of different triangular shapes, only three shapes seem suitable for folding puzzles: equilateral triangles, isosceles right triangles, and 60o-right triangles.Apparently my assertion was insufficient for mathematicians at Millersville State University, in Pennsylvania, so they set out to prove as their Theorem 1:A polygon generating an edge tessellation is either a regular hexagon; a 60o-90o-120o kite; a rectangle; a 120o-rhombus; a rectangle; an equilateral, a 30o-right, an isosceles right, or a 120o-isosceles triangle.which in due course appeared inMatthew Kirby and Ronald Umble, "Edge tessellations and the stamp folding problem,"Dr. Kirby and Prof. Rumble characterized my assertion as a conjecture, which I guess made them feel comfortable providing a proof. I would prefer the term assertion rather than conjecture, since I had little doubt about its correctness. In any event, I did not see any surprises in their proof, but must nonetheless thank them for dotting the i's and crossing the t's in my assertion.
Mathematics Magazine, vol. 84 (2011), pp. 283-289.
Copyright 2014, Greg N. Frederickson.
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