In Italy, France and Britain "nine joined rings" became known as "the key without a lock," and binary code for the solution of each step of the nine rings can be generated by the Gray Code, invented only this century. The mathematical formula for its solution was deduced at a math contest in Moscow.
九連環放洋之後，先後在義、法、英等國被用為「不用鑰匙的鎖」；而運用廿世紀發現的「格雷碼反射循環數列」，可以編出解九連環每一步驟的二進位代碼；莫斯科數學競試則曾以數學歸納法導出拆解的公式。