Pair Hands (2)
You should remember how to aim at Chiitoitsu, and the basic theory behind it.
1. The Branching Point Between Chiitoitsu and Regular Meld Hands
As a rule, when a regular meld hand and a Chiitoitsu hand are at the same shanten number,
the regular meld hand has a wider acceptance and reaches tenpai more easily.
So if the meld hand is lower in shanten than the Chiitoitsu route,
for example if Chiitoitsu is two-shanten while the meld hand is one-shanten,
then you should narrow your focus to the meld hand.
Example 1
Tsumo 
Dora
In Example 1, of course, you do not look at Chiitoitsu at all.
You simply discard 
.
Example 2
Tsumo Dora
But what about a hand like Example 2,
where Chiitoitsu is one-shanten while the regular meld hand is two-shanten?
From a technique point of view:
- Meld-hand technique -> discard
- Chiitoitsu technique -> discard
and throw the dora indicator tile
It used to be said that you should decide on one route early,
but the modern mainstream approach is to keep both the regular meld hand and the Chiitoitsu route alive as you play.
Discarding 
is a move that stays flexible for both.
The main line is still Tanyao + two dora,
but you should not throw away the possibility of reaching a Chiitoitsu tenpai
if you draw tiles such as 
.
Some people might criticize this as indecisive,
but I think discarding is the correct answer.
Example 3
Tsumo Dora 
If you only think about the regular meld hand in Example 3,
then naturally you tsumogiri 
.
But discarding 
looks better,
because it keeps both routes available.
Theory Summary
When the meld hand is awkward, keep the Chiitoitsu option alive.
Example 4
Tsumo Dora
What about Example 4?
If you want to preserve both routes,
you would cut 
.
That discard is not exactly wrong,
but the shape in Example 4 is already good enough that
even if you leave the Chiitoitsu possibility open, the hand is still likely to settle as a regular meld hand anyway.
So here the best discard is to focus on the regular meld hand,
cut ,
and lock in the dora meld.
2. Chiitoitsu Waits
Example 5
Tsumo
People often say that you should riichi as early as possible.
But immediately riichi'ing Example 5 is very questionable.
No matter which tile you wait on, it is not an easy hand to win.
Even if you had a 
,
riichi on a 
tanki is still poor.
A tanki wait only has three winning tiles to begin with.
When there are only three, you should not choose a tile that is hard to ron on top of that.
So what kind of tile should you choose for a tanki wait?
| Honor tiles | As a rule, wait on honor tiles that are easy to discard. An honor tile of which one copy is already visible in the pond is especially ideal. You can aim for both ron and tsumo. |
| 1s and 9s | These are also effective because they are easier to discard. 2s and 8s are not bad either. |
| Suji trap | This is for when you want to target ron. Even among suji traps, cutting a 4 and waiting on 1 is more effective than cutting a 4 and waiting on 7. |
| Kabe trap | For example, if all four copies of 3-pin are visible, you wait on 1-pin or 2-pin. Opponents may cut them thinking they are no-chance tiles. This is even stronger than a suji trap, and you can still expect tsumo. |
| Dora | 6400 points even in dama, and with riichi plus tsumo it can reach haneman. Useful when you want to win a big hand. |
A tanki wait lets you consciously aim for ron.
A tanki on an unneeded wind of which one copy is already visible in the pond is an excellent wait.
Example 6
Tsumo
If 
is still live,
while one copy of 
is already visible,
then you should riichi on the tanki.
The wait counts are only three tiles versus two tiles,
but the difference in ease of winning is enormous.
Theory Summary
When taking a tanki wait, deliberately choose a tile that is easier for opponents to discard.
Original Japanese page: http://beginners.biz/teyaku/teyaku10.html