Kock, A., & Mikkelsen, C. J. (1974). Topos-theoretic factorization of non-standard extensions. In A. Hurd & P. Loeb (Eds.), Victoria Symposium on Nonstandard Analysis (pp. 122–143). Springer Berlin Heidelberg. 
@inproceedings{kock-mikkelsen:1974,
  title = {Topos-theoretic factorization of non-standard extensions},
  author = {Kock, Anders and Mikkelsen, Chr. Juul},
  year = {1974},
  booktitle = {Victoria Symposium on Nonstandard Analysis},
  publisher = {Springer Berlin Heidelberg},
  address = {Berlin, Heidelberg},
  pages = {122--143},
  isbn = {978-3-540-37928-7},
  editor = {Hurd, Albert and Loeb, Peter}
}