I think the original proposition is just a tautology. What does it mean to "know" something? I think it is equivalent to being able to complete an "exercise".

I think the original proposition is just a tautology. What does it mean to "know" something? I think it is equivalent to being able to complete an "exercise". The fallacy here is thinking that the exercises in a book are special and must be completed and/or that you must have completed one before you could complete another outside the book.