(This is secon part of UmaiKeiki’s defense guide — Betaori and Suji posted in Osamuko’s Mahjong Blog)
Suji is one of the more complex theories in Mahjong. There are many variations and types of Suji, but it all boils down to one basic goal: to identify which Ryanmen waits are safe and which are dangerous.
Ordinary Suji are the tiles that complete Ryanmen waits.