The solution here https://github.com/total-typescript/typescript-generics-workshop/blob/main/src/04-generics-advanced/19-generic-interfaces-with-functions.solution.ts gives a Typescript error even though it passes all the tests: <img width="1146" alt="image" src="https://user-images.githubusercontent.com/8728285/224511181-eb16cd11-c183-480d-8f2f-b8187d8aa688.png"> Changing https://github.com/total-typescript/typescript-generics-workshop/blob/main/src/04-generics-advanced/19-generic-interfaces-with-functions.solution.ts#L8 to ```typescript clone: <U>(transform: (elem: T | undefined) => U) => Cache<U>; ``` seems to fix the issue