Important complex taatsu(1)

Source: http://blog.jpmahjong.net/read.php/506.htm

The taatsu mentioned in the previous article, are isolated and easy to spot taatsu. This time, we'll go through some common complex taatsu.

1. 4556 shape
The most common mistake made by beginners, is to see this as [456 shuntsu + isolated 5], and discard 5 too early. In truth, this shape should be seen as two ryanmen 45 + 56, allowing 3467 to be added into the hand. It also allows a good chance of getting ippeiko. In Japanese mahjong, it's a shape that is highly valuable. If there's a shape this like this in my hand, I won't easily dismantle it.

2. 4567 shape
The logic is the same here, this shape should be viewed as two ryanmen 45 + 67. This shape can evolve into many shapes. You can draw 56 to form a mentsu + ryanmen, draw 38 for a three sided wait, draw 47 to form a jantou + mentsu. It's value is not lower than the previous 4556.

3. 4456 shape
This is a toitsu + 56 ryanmen shape, there are quite a number of effective tiles. However, since there's a large probability of not forming a good ryanmen, it's not as valuable as the previous two shapes, but it's still a good shape.

4. 3567 shape
This is a shape that even intermediate players would sometimes forget. We can view it as 35 + 67. There are 6 useful tiles of this shape: 1, 2, 3, 4, 5, 8. Among them, 1, 5, 8 will create a kanchan. It's value is lower than 4456.

5. 4445 shape
This shape is no stranger to those who play mahjong, this is a common 3 sided wait shape. But if the hand is not in tenpai, the value of this shape is normal.
This shape is incapable of giving you two mentsu, at the most it'll give a jantou + mentsu. The important thing to remember, is that you need 4 mentsu in order to win, while you only need 1 jantou. Therefore, your need of mentsu is much higher than that of jantou. In fact, when you have many toitsu in your hand, this 5 here will often become a useless tile.