Mr. Ling has got to be the best teacher I've ever had. Not that I haven't had other great teachers, but they had it easier, since either the course subject or the level of difficulty they chose were far less demanding than Mr. Ling's standards. Let's spell it out: His level of teaching calculus IS hard. I found it terribly difficult. But if you put in a ton of work, he'll take you places. And the point is - he DOES take you there. For someone, who has a lot of trouble with math and never really found any inspiration in math (I just wanted to get the right result and pass the class), his lectures were truly awesome.