#1907

Henry Dudeney (1907) — Four Hinged Pieces That Turn a Triangle Into a Square

In 1907, English puzzle maker Henry Dudeney published, within The Canterbury Puzzles, the Haberdasher's Puzzle: cutting an equilateral triangle into just four pieces that reform into a square. Hinged together, the pieces could transform with a single fold, and the dissection drew attention in its day -- yet the proof that four pieces were truly minimal remained unresolved for a surprisingly long time, settled only by a 2024 computational-geometry paper. Tracing Dudeney's rivalry with Sam Loyd and his rediscovery through Martin Gardner, this piece rereads how a paper puzzle took 117 years to reach computer science.