Originally published in:
The Steenrod Algebra and its Applications,
Springer Lecture Notes in Mathematics Vol. 168,
© Springer-Verlag, 1970 and used by
permission.
Keywords: Concrete categories, homotopy theory
2000 MSC: 18B30, 55P15
Republished in:
Reprints in Theory and Applications of Categories,
No. 6 (2004) pp 1-10
http://www.tac.mta.ca/tac/reprints/articles/6/tr6.dvi
http://www.tac.mta.ca/tac/reprints/articles/6/tr6.ps
http://www.tac.mta.ca/tac/reprints/articles/6/tr6.pdf