they seem to me also to be exceptionally good books, and unbeatable at the price. The price of a textbook often depends on the ease of reading for the modern student, which is quite a different thing from the mathematical quality of the book.
Thus excellent books from the past, when readers were expected to have some intelligence and background, and be willing to work, are often phased out of the modern classroom, and not selling well, wind up as 10 dollar dover editions.
these are often far superior to what is out there now for 100 dollars. I am currently searching for a suitable book from which to teach differential equations, and there are several wonderful dover books under 20 dollars.
i just bought an out of print dover edition of hurewicz great lectures on the subject for 4 dollars. Another classic by Tenenbaum and Pollard that I have not yet seen goes for 10 or 15 dollars, while highly inferior modern boks sell for over 100 dollars.
I am sick of this exploitation of the student body by publishers, and am trying to use more dover books in class, but the inability of the many members of the modern generation of students to read writing which is not dumbed down, makes it harder.
One of my first dover books was the great treatise on electricity and magnetism of Maxwell!
Not only are the books better, but the publications valeus were always better too, the paper of higher quality and the pages bound in permanently sewn signatures.