"Dad was a teacher, too, and he also couldn't bear forcing his students to pay for new editions of a textbook. So he wrote his own. Students could print copies at cost in the print shop. I've continued the tradition of writing my own books and putting them online for free for the students."

Thanks for that. My professors were in part like yours. But some other professors (I think it was about MBA folks, not IT people) apparently urge everyone to buy their really expensive book. And if you did not, you would have no idea about the weird case in chapter 2, he makes the exams about ..