This article is very well written, but I must object to the implications of the statement that "no-one in the world today completely understands the whole proof." Of course, complete understanding is a high benchmark to set. But I would argue that Thompson, Aschbacher and Lyons understand the proof at least as well as Danny Gorenstein did, and Steve Smith and I (and probably several others) come pretty close. See our book which received the AMS Steele Prize for Mathematical Exposition. Danny Gorenstein deserves enormous credit for conceiving and daring to articulate the strategy of the proof back in 1971-72. But his overall perspective did not die with him.

## understanding the classification theorem

This article is very well written, but I must object to the implications of the statement that "no-one in the world today completely understands the whole proof." Of course, complete understanding is a high benchmark to set. But I would argue that Thompson, Aschbacher and Lyons understand the proof at least as well as Danny Gorenstein did, and Steve Smith and I (and probably several others) come pretty close. See our book which received the AMS Steele Prize for Mathematical Exposition. Danny Gorenstein deserves enormous credit for conceiving and daring to articulate the strategy of the proof back in 1971-72. But his overall perspective did not die with him.

Ron Solomon