equivariant Whitehead theorem



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The equivariant Whitehead theorem is the generalization of the Whitehead theorem from (stable) homotopy to (stable) equivariant homotopy theory:

Assume that the equivariance group be a compact Lie group (Matumoto 71, James-Segal 78, Waner 80). (This assumption is used, e.g. in Waner 80, Rem. 7.4, Shah 10, Rem. 1.2, to guarantee that Cartesian products of coset spaces G/HG/H are themselves G-CW-complexes, which follows for compact Lie groups, e.g. by the equivariant triangulation theorem.)

Then: GG-homotopy equivalences f:XYf \colon X \longrightarrow Y between G-CW complexes are equivalent to maps that induce weak homotopy equivalences f H:X HY Hf^H \colon X^H \longrightarrow Y^H on all fixed point spaces for all closed subgroups HGH \hookrightarrow G.

This is due to Matumoto 71, Thm. 5.3 Waner 80, Theorem 3.4, see also James-Segal 78, Thm. 1.1 with Kwasik 81, review in Shah 10, Blumberg 17, Cor. 1.2.14.

An analogous statement holds in stable equivariant homotopy theory:

For maps F:EFF \colon E \longrightarrow F between genuine G-spectra, they are weak equivalences (isomorphisms in the equivariant stable homotopy category) if they induce isomorphisms on all equivariant homotopy group Mackey functors π n(f):π n(E)π n(F)\pi_n(f)\colon \pi_n(E) \longrightarrow \pi_n(F) (e. g. Greenlees-May 95, theorem 2.4, Bohmann, theorem 3.2).


Proof for general G-CW-complexes:

  • Takao Matumoto, Theorem 5.3 in: On GG-CW complexes and a theorem of JHC Whitehead, J. Fac. Sci. Univ. Tokyo Sect. IA 18, 363-374, 1971 (PDF)

  • Stefan Waner, Theorem 3.4 in: Equivariant Homotopy Theory and Milnor’s Theorem, Transactions of the American Mathematical Society Vol. 258, No. 2 (Apr., 1980), pp. 351-368 (jstor:1998061)

following a partial result in

  • Takao Matumoto, Lemma 4.3 in: Equivariant K-theory and Fredholm operators, J. Fac. Sci. Tokyo 18 (1971/72), 109-112 (pdf, pdf)

Review and Lecture notes:

A proof for GG-ANRs is due to:

Proof that these GG-ANRs have the equivariant homotopy type of G-CW-complexes (for GG a compact Lie group):

  • Slawomir Kwasik, On the Equivariant Homotopy Type of GG-ANR’s, Proceedings of the American Mathematical Society Vol. 83, No. 1 (Sep., 1981), pp. 193-194 (2 pages) (jstor:2043921)

Textbook account for GG-ANRs:

For the stable case:

Last revised on March 19, 2021 at 07:07:21. See the history of this page for a list of all contributions to it.