Yes. And the paragraph that most stood out to me was this: > If the task you are working on can be expressed as a pure function that simply processes input par

Yes. And the paragraph that most stood out to me was this: > If the task you are working on can be expressed as a pure function that simply processes input parameters into a return structure, it is easy to switch it out for different implementations. If it is a system that maintains internal state or has multiple entry points, you have to be a bit more careful about switching it in and out. If it is a gnarly mess with lots of internal callouts to other systems to maintain parallel state changes, then you have some cleanup to do before trying a parallel implementation. If you have clean interface boundaries, it's easy to have two versions of something coexisting. If you don't, you can't just change the component in question, you have to change the whole program, which means you can't go this route. It's not just about deciding to do two implementations of something, it's about writing your whole program in ways that facilitate this style of development (no side effects, etc.)