User blog comment:P進大好きbot/Kyodaisuutan System/@comment-35870936-20181003040133/@comment-35470197-20181003223251

I avoided to use "(undefined term) \(\times 0\)", which appears in your definition.

Also, I should have said that the contest allowed us only to use \(+, -, \times, \frac{1}{x}, x^y\), and \(x!\) unless we write the definition as an additional rule. Therefore I could not use \(|x|\). (I used it first, but the definition was rejected.) Yeah, the use of \(|x|\) helps us very much.