Ikkitsuukan
| Type | Yaku |
|---|---|
| Kanji | 一通 or 一気通貫 |
| English | Straight |
| Value |
2 han 1 han (open) |
| Speed | Fast |
| Difficulty | Easy |
Ikkitsuukan 「一気通貫」, or ittsu 「一通」 for short, is one of the standard yaku. This hand contains three tile groups in one suit of 1 through 9. By English terms, this hand can also be noted as a "straight", similar to the poker hand of the same name. This hand may be open or closed.
Tile diagram
Winning tile: 
or 
Open
Winning tile:
Formation
While the hand shows a complete 1-9 grouping from a particular suit, it is best to view the long cluster as three separate groups of: 123, 456, and 789. This is particularly useful to note when needing to open the hand with such a combination. For example, having tile groups of 123, 345, 678, and 789 does not compose this yaku, despite possessing all 1-9 in the hand.
Counter example
Waiting for: or 
In this counter example, the tiles 1-9 for one suit are in the hand. However, ittsu would not be counted. In fact, this hand is lacks any yaku. The manzu are not grouped as 123, 456, and 789. Instead, they are grouped as 123, 567, and 789. The 4-man function as the pair rather than belong to any of the sequences.
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 | |
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Ittsu requires three out of the four tile groups to be composed of sequences: 123, 456, and 789. That may only leave room for one tile group of any type, such as a triplet; and so, any yaku that requires more than one triplet is deemed incompatible.
With pinfu
Pinfu requires a wait pattern of either ryanmen (open wait) or ryanmenten (three sided open). Any other wait pattern disqualifies pinfu. Ryanmen waits on two tile types, while ryanmenten waits on three tile types. Both of these wait patterns regarding ittsu are subject to takame and yasume, where only one tile type produces a winning hand of higher value. Winning on that one tile would produce ittsu; while the others do not. However, this problem is completely averted if the hand contains the full 1-9 pattern. Thus, the waiting tiles depend on the extra tile group, which renders the problem moot.
With honitsu and chinitsu
The development of honitsu and chinitsu with ittsu is made easier, when nine tiles (1-9) out of the thirteen of the hand is already single suited. That leaves the remaining four (plus one winning tile) to be composed of the same suit or an honor tile. But once again, in the case of pinfu, takame and yakume may apply here, if applicable.
With closed hands, this combination produces some very powerful hands. With honitsu, the hand produces mangan; while it is haneman with chinitsu.
External links
- Ikkitsuukan in Japanese Wikipedia
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