Tenhou and chiihou: Difference between revisions

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In Riichi Mahjong, Tenhou (天鳳) is a Yakuman attained by completing a hand with the 14 starting tiles that one draws during one's dealer turn. The hand does not need to fulfill any other yaku, as it already meets the requirements with Menzen Tsumo.
{{Infobox yaku
|type        = Yakuman
|kanji      = 天和<br>地和
|english    = Heavenly hand<br>Earthly hand
|value      = Yakuman
|yakuSpeed  = Instant
|difficulty  = Luck
|yakuCombine = * All other standard yakuman patterns, except [[Suu kantsu]] and [[chihou]].
|gameExample = * [http://tenhou.net/0/?log=2013090503gm-0009-0000-7ec29a70&tw=3&ts=3 Tenhou] with [[kanchan]]
* [http://tenhou.net/0/?log=2014031516gm-00c1-0000-c0e23ee9&tw=1&ts=4 Chihou win]
* [http://tenhou.net/0/?log=2014031109gm-0029-0000-892f3104&tw=0&ts=11 As chiitoitsu]
* [http://tenhou.net/0/?log=2014031008gm-0029-0000-95234e4a&tw=2&ts=4 Sitting north]
}}
'''Tenhou''' {{kana|天和}} is a [[List of yaku#Yakuman|yakuman]] obtained by the dealer completing the hand on the first tile draw. In other words, the hand wins before the first tile discard. Any combination of 14 tiles that can win can score tenhou. Declaring [[kan]] (or [[kita]] in [[sanma]]) will invalidate the yakuman.
 
'''Chiihou''' {{kana|地和}} is similar to tenhou, except it is won by non-dealers winning on the first draw. In addition, any [[naki|tile call]] made by other players will invalidate chiihou. By definition, both yakuman can only win by tsumo; [[ron]] is not allowed.
 
==Formation==
Tenhou and chiihou are entirely dependent on luck. The player only needs to recognize a complete hand and declare it. Failure to do so may result in a lost opportunity to score this rare yakuman.
 
One pitfall is to declare [[riichi]], not recognizing that you had a winning hand.<ref>http://www.osamuko.com/delicious-riichi-button-must-click-it/</ref>  This is likely due to the temptation of calling [[double riichi]] before verifying the completeness of the hand.  This puts the hand into [[furiten]] immediately for calling riichi on a winning tile.  Therefore, it is necessary to check the hand before making such a dubious riichi call.
 
==Value==
Tenhou applies to dealer seats only, so therefore, it is always 48,000 points unless combined with [[Multiple_yakuman|another yakuman]].  Likewise, chiihou applies to non-dealers valued at 32,000 points.  Both must be won via [[tsumo]].
 
==Renhou==
{{Main|Renhou}}
A related [[optional yaku]] is '''renhou'''. Assuming this yaku is used: if a player wins via ron before their first draw, and before any calls, then this yaku(man) is scored. Depending on rule variation, it may score as a [[mangan]] (or other value), not a yakuman.
 
==Probability==
A randomly drawn hand of 14 tiles has about a one in 330,000 (~0.0003%) chance of being a valid mahjong hand and thus qualifying for tenhou or chiihou.<ref>http://www10.plala.or.jp/rascalhp/mjmath.htm</ref> Based on a [[wikipedia:Monte Carlo method|Monte Carlo simulation]] of one hundred billion (100,000,000,000) such randomly drawn hands, the distribution of outcomes is as follows:
{| class="wikitable"
|-
! Outcome !! Occurences
|-
| Not a winning hand || 99,999,696,816
|-
| Tenhou in standard form || 267,813
|-
| Tenhou in [[chiitoitsu]] form || 35,351
|-
| Tenhou with [[suuankou]] || 43
|-
| Tenhou with [[kokushi musou]] || 20
|-
| Tenhou with [[daisangen]] || 1
|-
| Tenhou with [[chuuren poutou]] || 1
|}
 
==References==
{{references}}
 
==External links==
[[Image:Real Tenhou.jpg|thumb|250px|right|A real tenhou.]]
{{jpwiki|天和|Tenhou}}
{{jpwiki|地和|Chiihou}}
{{Youtube| url        = https://www.youtube.com/watch?v=G3Lvwp-2duE| linkname    = 【天和】世界初!生放送対局にて炸裂!【役満】| description = Tenhou scored at an [[RMU]] event.}}
* [https://twitter.com/UMP45_mw3/status/1355048481602199556 天和国士無双十三面待ち]
: Tenhou combined with [[kokushi musou]] in the "Battle of Asura" mode of [[Majsoul|Mahjong Soul]] which allows players to exchange tiles before the hand starts. In this case, the game counts kokushi musou as the 13-way wait variant, combining with tenhou for a triple yakuman—144,000 points.
 
[[Category:Yakuman]]
 
{{Navbox yaku}}
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