Trick Riichi is strong

 

Answer

Commentary

Discarding 4 and waiting 7 is called Moro(completely) Hikkake (trick).

This is relatively strong method.

In the rule of including red Dora,  expected value of waiting 5 is a little bit higher than others.

Even with that, winning rate of this trick is strong statistically.

Especially, It's even more effective when used for following Riichi.

The players who don't have safety tile will discard, and it is too difficult to have common safety tile for multi player.

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This is "Kyoho" ; japanese variety.

One of the Japanese autumn scenery.