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ID13-Discarded Tile Cannot Be Used in a Joker Exchange
Question: Can I use the tile I called to do a Joker Exchange?
Answer: Discarded tiles cannot be called and then used to do a joker exchange. Joker exchanges are permitted only when a player picks the natural tile from the wall or already has the natural tile in their rack. This ruling is not found in Mah Jongg Made Easy.
Source: NMJL Bulletin Q&A 2020