I'm looking into buying both volumes of Apostol's Calculus, to "read around my subject" as Ian Stewart says, while taking Calculus courses that use James Stewart's text. I've found the hardcover versions used for around $80-90, but I've also found a paperback edition where both volumes come for around $30. The text is supposedly the same as the hard cover, but all in black and white. Has anyone had experience with the different versions? Is the paperback version really the same? The sellers all seem to be from different countries, so I'm a little wary.