Life In 19x19

This one is for the stronger players. For me, at least, it was a new wrinkle on an old classic, and seems to have been so even for a pro.

In the position below, Black (Hayashi Yutaro) caught White (Kosugi Tei) by surprise with the triangled move. Kosugi said of it: "When Black got to play 71 I was in trouble. But I had to admire it - it came precisely from studying the [Gokyo] Shumyo." Why was it so good and what is the outcome?



Generous hint: For kyus: Gokyo Shumyo is the classic (1812) repository for these sorts of small corner positions, and is routinely recommended for kyu players. But I think this example illustrates it can be studied with profit even by pros.

This shape, or very similar, also came up in a Malkovich game here. Maybe Magicwand vs topazg iirc. drmwc (Matt Cocke, UK 5d) pointed out how a hane like this meant some group I had dismissed (without reading but common shape like L or J group recognition) wasn't actually totally dead.