Suji: Difference between revisions

'''Suji''' {{kana|筋}} involves the general inference of discarded tiles, when determining safe tiles.  The term alone points towards the principle of utilizing the "mahjong intervals". This applies to the numbered suits: [[souzu]], [[pinzu]], and [[manzu]]. While these three suits are numbered 1 through 9, the numbers may be arranged in a square fashion to determine the "intervals". The purpose is to deduce and/or determine tiles waiting via [[ryanmen|open]] [[machi|waits]]. The intervals themselves are based on the three-tile [[shuntsu|sequential groupings]]. Tiles along the intervals mark needed tiles to complete particular sequences. Reading the numbers to the right across, the three main intervals are 1-4-7, 2-5-8, and 3-6-9. Naturally, numbers within each interval can be paired such as 1-4 and 2-5. Other references to suji are available, such as matagi suji and ura suji.

The intervals for suji apply to any of the numbered suits.  Nine types of intervals are available.  For these examples, each of the three suits are used; but they apply to all of them.  Four tile patterns particularly utilize these intervals: [[ryanmen]], [[ryanmenten]], [[nobetan]], and [[sanmentan]].  In the following table, only the first two are examined.

Defending using suji essentially presumes a player to be utilizing either the wait pattern of [[ryanmen]], [[ryanmenten]], [[nobetan]], [[sanmentan]], or some other variation. Under the rule of [[furiten]], if a player discarded a waiting tile, then the player's ability to call "ron" is disabled.  Therefore, certain tile discards may rule out certain mahjong intervals.

For example, take the 1-4-7 interval. If a 4 is discarded, this makes 1 and 7 safer, since if the opponent has a 23 or 56 as their final shape, they would be furiten on the 4. Note that a 7 being present does not necessarily make a 4 safe, as they could still have a 23. Therefore, both a 1 and 7 need to be present in order for 4 to be safer. In such a situation, the 4 is referred to being nakasuji. The same applies to the other intervals.

Of course, one should not be necessarily dependent on these intervals alone, as some waiting patterns are immune to suji, such as a [[kanchan]] or [[shanpon]]. A [[toitoi]] hand is immune to suji.

Because of this, not all suji tiles are equally safe. Suji terminals (1 and 9) are the safest, as the only shapes that can be waiting on them are a [[tanki]] or [[shanpon]]. Nakasuji (4, 5, and 6) are the next safest, as they add the possibility of a [[kanchan]]. Suji 2 and 8 are roughly equivalent to nakasuji. Finally, suji 3 and 7 are the most dangerous (though still reasonably safe), as they add the chance of a [[penchan]] wait.

This doesn't apply to the riichi tile. The suji of the riichi tile is generally agreed to be dangerous, thanks to the strength of ryankan shapes. See the [[#Offense|Offense]] section for more information.

However, in a game with red fives, the player has an incentive to keep the red five. If they have a 135 shape, and the 5 is red, they would likely discard the 1 in order to keep the dora. Or, with a 246 shape, they could take the 46 shape and hope to win on the red five. 456 could be viewed as more dangerous in this ruleset, especially if you can't see the red five in the suit of your 2 or 8. As a side note, this is why the suji of a red five is seen as especially safe.

For defense, eighteen different suji are in consideration as listed above.  Six basic suji multiplied by the three suits produces the count of eighteen suji.  After all, hand shapes frequently depend on ryanmen to win, as they are the most efficient and have the widest range of waiting tiles involving just two tiles in the hand.  By counting the number of visible suji, players can determine roughly how risky it is to discard a dangerous tile.