unexpected token ',' means "that comma is nonsense". Lean 3 had commas at the end of lines, Lean 4 does not. Delete the comma, and then you'll get another error unexpected token ',' which means you should delete that comma too. Repeat a third time. You'll then get an unknown tactic error because you're using the Lean 3 cases syntax, not the Lean 4 cases syntax. Did an LLM which can't tell the difference between Lean 3 and Lean 4 write this code by any chance? You can change cases to cases'. You'll then get another error about a comma etc etc. Basically your code doesn't work because it's full of syntax errors.