# 约束 whisper 只输出「乘法口诀答案」：可选(两因数[得]) + 一个规范数字
root    ::= prefix? product
prefix  ::= sd sd "得"?
product ::= cn | ar
sd      ::= "一" | "二" | "三" | "四" | "五" | "六" | "七" | "八" | "九" | [0-9]
cn      ::= tens | teen | unit | "十"
unit    ::= "零" | "一" | "二" | "三" | "四" | "五" | "六" | "七" | "八" | "九"
teen    ::= "十" unit
tens    ::= unit "十" unit?
ar      ::= [0-9] [0-9]?