I disagree. I used to do a lot of math years ago. If you gave me some problems to do now I probably wouldn't be able to recall exactly how to solve them. But if

I disagree. I used to do a lot of math years ago. If you gave me some problems to do now I probably wouldn't be able to recall exactly how to solve them. But if you give me a written solution I will still be able to give you with 100% confidence a confirmation that it is correct. This is what it means to understand something. It's like P Vs NP. I don't need to find the solution, I just need to be able to verify _a_ solution.