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Chankan (view source)

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[[image:Chankan.png|250px|thumb|[http://tenhou.net/0/?log=2012112813gm-0009-7447-af4e435f&tw=2&ts=8 Chankan example], where the player declared ron on 1-pin and all four are shown as a kan.]]
[[image:Chankan.png|250px|thumb|[http://tenhou.net/0/?log=2012112813gm-0009-7447-af4e435f&tw=2&ts=8 Chankan example], where the player declared ron on 1-pin and all four are shown as a kan.]]


Alternatively, this yaku may be referred to as "robbing a kan".  [[Tenpai]] for chankan must involve a hand, in which one of the [[machi|waiting tiles]] has been called as [[naki|pon]] by another player.  Any tenpai hand works for chankan, even "yakuless" hands.  As long as the waiting tile has been called for [[naki|pon]] earlier and then the player calls for an added kan, this creates a time for a player to claim the added tile for a win.  Naturally, waits involving [[jihai|honor tiles]] do not work in this situation.
Alternatively, this yaku may be referred to as "robbing a kan".  [[Tenpai]] for chankan must involve a hand, in which one of the [[machi|waiting tiles]] has been called as [[naki|pon]] by another player.  Any tenpai hand works for chankan, even for an otherwise "yakuless" hand.  As long as the waiting tile has been called for [[naki|pon]] earlier and then the player calls for an added kan, this creates a time for a player to claim the added tile for a win.  Naturally, waits involving [[jihai|honor tiles]] do not work in this situation.


While the call for kan reveals additional [[dora]], in the form of kan-dora, the call for chankan interrupts the process for kan.  Therefore, additional dora is not revealed.
While the call for kan reveals additional [[dora]], in the form of kan-dora, the call for chankan interrupts the process for kan.  Therefore, additional dora is not revealed.
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As defined, chankan can only be achieved when a [[minkou]] (open triplet) is upgraded to a ''shouminkan''.  In other words, a player had called pon earlier and then drew the 4th tile, for the kan.  If another player is tenpai for that tile, then the player may declare ron.  To some degree, the added kan may be viewed as a discard in this case.
As defined, chankan can only be achieved when a [[minkou]] (open triplet) is upgraded to a ''shouminkan''.  In other words, a player had called pon earlier and then drew the 4th tile, for the kan.  If another player is tenpai for that tile, then the player may declare ron.  To some degree, the added kan may be viewed as a discard in this case.


So, when it comes to [[machi]] (wait patterns), only three basic types can be used for chankan: [[penchan]], [[kanchan]], and [[ryanmen]]. Some patterns that utilize any of these three may also apply. This is simply due to the number of tiles remaining (just one), for every minkou.  So, tile patterns involving [[shanpon]] and [[tanki]] are impossible for chankan, as they each possess tiles necessary for kan calls.
So, when it comes to [[machi]] (wait patterns), only three basic types can be used for chankan: [[penchan]], [[kanchan]], and [[ryanmen]]. To achieve chankan, all four copies of a tile would've needed to been in another player's hand. Therefore, a hand winning with chankan must not have any copies of that tile. This forbids tile patterns involving [[shapon]] and [[tanki]], as both types of wait require at least one copy of that tile.


In the case for [[kokushi musou]], the hand is tenpai for kokushi with one of the 13-tile types already paired; and it is waiting for the last tile type for completion.  An exception to kan calls involving [[ankan]] (closed kan) is made.
In the case for [[kokushi musou]], the hand is tenpai for kokushi with one of the 13-tile types already paired; and it is waiting for the last tile type for completion.  An exception to kan calls involving [[ankan]] (closed kan) is made.
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{{Yaku compatibility table|CHK}}
{{Yaku compatibility table|CHK}}


Essentially, chankan combines yaku, that utilizes the [[machi|tile waits]] of either [[ryanmen]] or [[kanchan]]. Either of these two tile waits do not include the waiting tile in the hand.  That excludes [[toitoi]], [[chiitoitsu]], and [[honroutou]]. These three require the tile waits of either [[shanpon]] or [[tanki]]; and so, the fourth tile to invoke kan is used in another player's hand. As for [[ryanpeikou]], this hand may use ryanmen for completion.  However, the tile requirement for ryanpeikou is already in the hand.  Otherwise, chankan invoked with a ryanpeikou tenpai hand would only count for [[iipeikou]].
Excluding kokushi musou, chankan requires at least one sequence in the hand, because waits to complete a pair (tanki) or triplet (shapon) would be impossible. This excludes [[toitoi]], [[chiitoitsu]], and [[honroutou]]. [[Ryanpeikou]] is also not allowed, due to the tile requirement. A ryanpeikou tenpai requires at least one copy of the winning tile, and in order for an opponent to call kan in the first place, you must have no copies of said winning tile.


As for [[rinshan]], [[haitei]], [[houtei]], and [[mentsumo]], it is physicially impossible to combine any of these four with chankan.  In the case for rinshan, the possibility to combine with chankan is outright impossible, as rinshan is defined by winning from the dead wall tile draw.  In the case of haitei and houtei, a player cannot call kan, when the dead wall cannot be maintained at 14-tiles.  This case occurs, at the last allowable tile draw of the hand.
As for [[rinshan]], [[haitei]], [[houtei]], and [[mentsumo]], it is physicially impossible to combine any of these four with chankan.  In the case for rinshan, the possibility to combine with chankan is outright impossible, as rinshan is defined by winning from the dead wall tile draw.  In the case of haitei and houtei, a player cannot call kan, when the dead wall cannot be maintained at 14-tiles.  This case occurs, at the last allowable tile draw of the hand.
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