The Chinese student (was his name Bo?) told the professor what the problem was. Greenbaum looked down. He studied the page. Then he looked up and said to to the Chinese student.
‘Thank you very much. You are right. I will send a note to the publisher to make the change in the next edition.’
And there we have it. One of the greatest authorities working in English Grammer, with the book that won him the OM, conceding to a non-native speaker that he had made a mistake and thanking him for pointing it out.