This is something I've been working on for a while now; although it seems trivial, I am confused. I can't seem to find the error.
Originally I thought the problem was with the base case, then I noticed the peculiar structure given to the proof where any two numbers $a, b \leq n$ are equal, then I thought it was something with the general assumption. Unfortunately, I don't get where the problem is.
Can someone HINT me? I don't want the full answer I want to figure it out myself.