Encountered a rare musical symbol in section 7 of guqin tune 秋塞吟

Encountered this symbol in section 7 of the 古琴 guqin tune 秋塞吟 Qiu Sai Yin (Autumn Scenery Beyond The Great Wall). Yes, I have tried to check some eBooks but due to my incompetence, I could not find it. haha

Thanks to Charles R. Tsua's help, now I know how to play this symbol. According to him, “豆 = 逗. Played as 立 but during the 乚.” Hooray!

Fyi, English language versions of ebooks that explain how to play guqin musical notation symbols can be purchased from Lulu.com