• Source: Whitehead conjecture

The Whitehead conjecture (also known as the Whitehead asphericity conjecture) is a claim in algebraic topology. It was formulated by J. H. C. Whitehead in 1941. It states that every connected subcomplex of a two-dimensional aspherical CW complex is aspherical.
A group presentation



G
=
(
S
∣
R
)


{\displaystyle G=(S\mid R)}

is called aspherical if the two-dimensional CW complex



K
(
S
∣
R
)


{\displaystyle K(S\mid R)}

associated with this presentation is aspherical or, equivalently, if




π

2


(
K
(
S
∣
R
)
)
=
0


{\displaystyle \pi _{2}(K(S\mid R))=0}

. The Whitehead conjecture is equivalent to the conjecture that every sub-presentation of an aspherical presentation is aspherical.
In 1997, Mladen Bestvina and Noel Brady constructed a group G so that either G is a counterexample to the Eilenberg–Ganea conjecture, or there must be a counterexample to the Whitehead conjecture; in other words, it is not possible for both conjectures to be true.




References


Whitehead, J. H. C. (1941). "On adding relations to homotopy groups". Annals of Mathematics. 2nd Ser. 42 (2): 409–428. doi:10.2307/1968907. JSTOR 1968907. MR 0004123.
Bestvina, Mladen; Brady, Noel (1997). "Morse theory and finiteness properties of groups". Inventiones Mathematicae. 129 (3): 445–470. Bibcode:1997InMat.129..445B. doi:10.1007/s002220050168. MR 1465330. S2CID 120422255.

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