provide diffs of new editions of textbooks for those with older editions, especially the psets

It's common to have an old edition of a textbooks (borrowing from friend who already took it, for sale cheap, retaking class, etc.), but this at times plays havoc with taking the class, not only because new chapters are absent, but also because psets are changed, renumbered, moved, etc. I realize this may be difficult because the publishers have little incentive to cooperate, but providing free or cheap supplements (likely just digital) with the differences between editions noted would make students' lives much simpler when using an older edition.