Henry Ernest Dudeney/Modern Puzzles/140 - The Four-Colour Map Theorem/Mistake

Source Work

 * Geometrical Problems
 * Varous Geometrical Puzzles
 * $140$ -- The Four-Colour Map Theorem
 * $140$ -- The Four-Colour Map Theorem

Correction
's analysis of this problem does not constitute a proof.

explains it in his $1968$ repackaging as follows: