https://github.com/Lean-zh/fp-lean-zh/blob/c0597a1d8e4333d10a0981b9bee77385f9d54712/functional-programming-lean/src/type-classes/standard-classes.md?plain=1#L363 当发生这种事情的时候,就手写一个 `Ord` 实例把。 把 -> 吧