This is interesting, but as the author acknowledges, not legal in modern games. Another famous position which relies on (legal) underpromotion: https://en.wiki

This is interesting, but as the author acknowledges, not legal in modern games. Another famous position which relies on (legal) underpromotion: https://en.wikipedia.org/wiki/Saavedra_position https://en.wikipedia.org/wiki/Saavedra_position