Saunders MacLane (1909-2005) was one of the founders of category theory, with Samuel Eilenberg. Their 1945 paper General Theory of Natural Equivalences introduced category theory with the notions of categories, functors and natural transformations, motivated by formalizing the concept of dual objects.
Further with Eilenberg he developed of the strong links with group theory and group cohomology.
With Henry Whitehead he gave the first algebraic description of the homotopy 2-type of a space.
Colin McLarty: The Last Mathematician from Hilbert’s Göttingen: Saunders Mac Lane as Philosopher of Mathematics, Brit. J. Phil. Sci. (2007) [pdf]
On group extensions and group homology via Ext/Tor-functors:
Introducing category theory:
Introducing abstract group cohomology:
Introducing Eilenberg-MacLane spaces:
Samuel Eilenberg, Saunders Mac Lane, On the Groups , I, Annals of Mathematics Second Series, Vol. 58, No. 1 (Jul., 1953), pp. 55-106 (jstor:1969820)
Samuel Eilenberg, Saunders Mac Lane, On the Groups , II: Methods of Computation, Annals of Mathematics Second Series, Vol. 60, No. 1 (Jul., 1954), pp. 49-139 (jstor:1969702)
Samuel Eilenberg, Saunders Mac Lane, On the Groups , III: Operations and Obstructions, Annals of Mathematics Second Series, Vol. 60, No. 3 (Nov., 1954), pp. 513-557 (jstor:1969849)
Introducing the simplicial classifying space construction :
On homotopy 2-types (N.B. their 3-type is the modern 2-type)
On Grothendieck universes in the mathematical foundations of category theory:
On geometric realization of simplicial topological spaces for constructing classifying spaces, understood as simplicial coends in compactly generated topological spaces:
On category theory:
On some history of mathematics:
See also:
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