@book{maclane,
  author = {Mac Lane, Saunders},
  title = {Categories for the Working Mathematician},
  year = 1971,
  publisher = {Springer-Verlag New York, Inc.},
  langid = {english}
}
@book{joyofcats,
  author = {Adámek, Jiří and Herrlich, Horst and Strecker, George},
  title = {Abstract and Concrete Categories: The Joy of Cats},
  year = {1990},
  publisher = {John Wiley \& Sons, Inc.},
  langid = {english}
}