Kazuyuki SAWAMURA introduced Tengen-jutsu (an algebra developed during 13th century China), which was an algebra equation for a variable number and its numerical method of solution, in his book "Kokon Sanpo-ki" (Old and New Mathematics), and he further presented a problem that required an algebra equation containing various numbers that could not be solved using only Tengen-jutsu as an idai to the book.
沢村一之は『古今算法記』で中国の天元術、すなわち一変数の代数方程式とその数値的解法を導入し、また、同書の遺題で天元術では扱えない複数の変数をもった代数方程式を必要とする問題を提出した。