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ID42-East is Playing a Singles & Pair Hand with a Joker as First Discard
Scenario: If East is playing a singles & Pairs hand and their first tile is a Joker, it must be named, “Joker”. This is there was no previously discarded tile from which to name it.
Source: National Mah Jongg League Bulletin Q&A 1995 page 4, 2003
https://www.nationalmahjonggleague.org