Each letter of the alphabet has been put into one of three sets.

Set 1: A, F, H, K, M, N, P, Q, R, T, X, Y

Set 2: B, D, O

Set 3: C, E, G, I, J, L, S, U, V, W, Z

What is the rule for which set a letter goes into?

Hint: The solution has to do with the shape of the letter. Depending on the exact shape of I that you consider, I might belong in set 1 instead.

Submit your answer to Gene Wirchenko <genew@telus.net>. Your answer should be in the form of a proof. That means to show how your answer must be correct. **The deadline is Wednesday, January 25, 2017 at noon Pacific Time.** I will post the answer shortly after.