Ebook: Toposes, Triples and Theories

From the reviews: "Michael Barr, Charles Wells uses the most efficient tools to get at the central theorems. This is a very readable introduction to the subject … . no other book goes as concisely and comprehensively to all the aspects of toposes as this one. Category theory, algebra, logic, arithmetic, geometry, and cohomology all come in, in a well chosen perspective. … it remains the best single text on the subject." (Wordtrade, 2008)