> As an aside, line 511 is entered when it fails to find matching values with the current game state for all 19 boards and flipped boards. It seems like it was originally intended to be a comment using the REM command like 511 REM REMEMBER THE TERMINATION OF THIS LOOP IS IMPOSSIBLE, but perhaps that part was omitted during editing, so it just starts with REMEMBER.

Actually, that line does start with "511 REM". There was no requirement for REM to be followed by a space.

I didn't realize that! Thanks for the clarification.