Shousangen

Shousangen
Type	Yaku
Kanji	小三元
English	Small three dragons
Value	2 han (Consider as 4 han)
Speed	Medium
Difficulty	Medium

Shousangen 「小三元」 is a standard yaku, reliant on all three sangenpai. The hand is composed of two koutsu (triplet) and a jantou (pair) of the third type.

Tile pattern

agari :

Winning on yasume (cheaper winning tile), notice that winning on would give a daisangen yakuman instead.

Development

The hand requires two out of the four tile groups to be composed of dragon triplets, while the pair is always of the third type. That leaves two tile groups to be based off of any tile composition. Often enough but not always, such a hand may be tenpai for daisangen.

Compatability

Main article: Yaku compatability

^ Ippatsu requires riichi to be of any use.

	RCH	DRI	IPP^	SMO	TAN	PFU	IPK	ITT	YAK	SDJ	SDO	TOI	SNA	SNK	CHA	JUN	RPK	SSG	HRO	HON	CHN	CHI	RIN	HAI	HOU	CHK
SSG

Shousangen requires yakuhai, from the two groups of dragon tiles. Out of the regular four tile groups for a hand, two are dedicated for dragon tiles. So, this yaku has no room for the likes of ittsu, ryanpeikou, sanshoku, and sanshoku doukou. Each of those four yaku require at least three tile groups for their specific requirements. Naturally, tanyao, junchan, and chinitsu are incompatible because of the dragon tiles.

Value

In general, this yaku is noted as 2 han. However, it is impossible for this yaku to score without two instances of yakuhai from the two groups of sangenpai. In combination, this yaku will never produce a hand worth less than 4 han. Even with both sangenpai groups called open, that is a combination of 8 fu; and then there's 2 more fu from the sangenpai pair of the third type. This means that with a closed ron, or when playing with kiriage mangan, the hand will always score at least mangan; otherwise, the only way to avoid mangan is to avoid any other han and fu and score exactly 4 han 30 fu.

The requirements to do so, assuming no additional yaku, are:

The hand must be won by ron, as a tsumo would score 2 fu.
The wait must be either a ryanmen or shanpon wait, as any other wait would score 2 fu.
Both of the other groups must be shuntsu of different suits. If either was a koutsu, it would score at least 2 fu.
Both of the yakuhai groups must be open, as they would score additional fu if closed. Note that as this is for the purposes of counting fu, if a group is completed by ron, it counts as being open.
Neither of the yakuhai groups may be kantsu, as they would score additional fu as kantsu.

Two examples scoring exactly 4 han 30 fu on a ron:

Agari: