↑ Hodges, GF (1976). “Middle shogi & how to play it”. Shogi (1): 10–12.
↑ The Middle Shogi Manual allows pieces to regain their promotability after they move once without promoting. However, the Japanese Chu Shogi Association uses a different promotion rule, where a piece can only promote on a non-capture when it enters the zone. Once in the zone pieces can only promote on captures. There is strong evidence from historic mating problems that this has always been the rule in Japan.
↑ http://www.chushogi-renmei.com/kouza/rule.htm rule 2.3 (" 三.両軍がともに駒を消耗しあい、駒枯れの状態になった場合、玉将２枚と成金１枚だけが盤面に残ったときは成金のある側が勝ちとなります。") An example of this is discussed in section 5.5 of the same page, second diagram.
