Dudeney's Cross-to-Isosceles-Right-Triangle Dissection
This Demonstration gives Dudeney's (1897) dissection of a four-piece hinged cross into an isosceles right triangle.
Henry Ernest Dudeney (1857-1930) was a self-educated English mathematician. Collections of his puzzles appeared in five books.
G. N. Frederickson, Dissections: Plane & Fancy, New York: Cambridge University Press, 1997.
G. N. Frederickson, Hinged Dissections: Swinging & Twisting, New York: Cambridge University Press, 2002 p. 19.