Tremontaine, first season from Serialbox (prequel to Ellen Kushner's "Swordspoint" and "Privilege of the Sword") is at 0.99 USD, at
https://www.bookbub.com/books/tremon...-lo?ebook_deal ,
https://www.kobo.com/ww/en/ebook/tremontaine and probably elsewhere.
Swordfighting, mathematics, intrigues, and chocolate!