Farmer's Hat

    Keywords: Shape, Go term

Chinese: 丁四 (ding1 si4)
Japanese: 陣笠 (jingasa)
Korean: 삿갓

Term and naming

Farmer's hat  

The farmer's hat is a Korean go term adapted into English. It is a shape named by analogy to the cone-shaped straw hat worn by medieval Japanese warriors and later farmers.


White's shape after W5 is called jingasa in Japanese, which corresponds to the Korean term (See [ext] here and [ext] here). However, jingasa is also defined as having two empty triangles (see [ext] here , [ext] here, and The Go Player's Almanac), which this shape does not (W1-W3-W5 are a "full" triangle), so there is some uncertainty about whether this example is correct usage.

The farmer's hat as a bad shape

The farmer's hat is essentially an empty triangle with an extra stone added to form a second empty triangle, and bad for the same reasons that the empty triangle is bad.

Bad shape  

The farmer's hat and in particular its empty triangle(s) is a heuristic to decide for or against variations that end up in such a shape, indicating the move or a prior move is a mistake:

Bad Shape  

Prior to the AI revolution W5 was classified as a mistake, and White was thought to either atari at a or make a ko at b.

Since the AI revolution, W5 is considered the best move locally. The real mistake is rather W3 which under most circumstances is played at c.

See Farmer's hat/evaluated with KataGo

The farmer's hat as a killable eye shape

The farmer's hat may also refer to the four-space, T-shaped killable eye shape.

Eye shape  

Please refer to pyramid four for this interpretation.

See also

Farmer's Hat last edited by Dieter on March 16, 2021 - 12:45
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