Hello,

    Prof. Harold Simmons' tutorial IMO are like a Russian matroshka doll ... first layer is for newbie ... inner layers require more sophistication. IMO a very subtle writer ... I have every book imaginable on cat theory and topos theory so I think can compare a little.

       1) http://www.cs.man.ac.uk/~hsimmons/BOOKS/books.html  ... an earlier version ... "An Intro to Category Theory in Four Easy Movements" ... this version delves a little into Topos Theory ... pretty subtle .. cool

       2) http://www.cs.man.ac.uk/~hsimmons/MAGIC-CATS/magic-cats.html  ... newer version which also has its cool merits IMO!

Regards, Vasili