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Homotopy theory is an important sub-field of algebraic topology. It is mainly concerned with the properties and structures of spaces which are invariant under homotopy. Chief among these are the homotopy groups of spaces, specifically those of spheres. Homotopy theory includes a broad set of ideas and techniques, such as cohomology theories, spectra and stable homotopy theory, model categories, spectral sequences, and classifying spaces.

4 votes

Identifying $d_1$ in the Atiyah-Hirzebruch-Serre spectral sequence

This is Theorem 4.8 in Chapter XIII of Whitehead, George W. Elements of homotopy theory. Graduate Texts in Mathematics, 61. Springer-Verlag, New York-Berlin, 1978. xxi+744 pp. ISBN: 0-387-90336-4 an …
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6 votes
Accepted

Loop-space functor on cohomology

If you are willing to read a little French, look at page 434 of Serre's "Homologie singuliere des espaces fibres" (1951). For an exercise in English, with a hint, try Exercise 2 on page 155 in Mosher …
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5 votes

Group completion of a monoid (braid groups)

See Proposition 1 in McDuff, D.; Segal, G. Homology fibrations and the "group-completion'' theorem. Invent. Math. 31 (1975/76), no. 3, 279–284.
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14 votes

What are some good examples of spectral sequences which degenerate after the first nontrivia...

Some examples with one nonzero family of differentials: The classical Adams spectral sequence for $j/p$, the connective image-of-J spectrum reduced mod $p$, collapses at $E_3$, by Theorems 4.5 (at $p= …
13 votes
Accepted

Derivations in the Steenrod algebra

The $D$ with $D(xy) = xD(y) + D(x)y$ are the primitives in the Steenrod algebra $A$, which are dual to the indecomposables $\xi_i$ in $A_* = F_2[\xi_i \mid i\ge1]$, so there is one such $D$ in each de …
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5 votes
Accepted

Does a complex-oriented $E_1$ ring spectrum (not assumed to have graded-commutative homotopy...

The initial example of such an $E$ is the Thom spectrum $M\xi$ associated to the $E_1$-map $\Omega \Sigma BU(1) \to BU$, studied by Baker and Richter in "Quasisymmetric functions from a topological po …
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1 vote

Reference for choosing a path lifting function?

(Not an answer, but long for a comment.) Spanier's "Algebraic Topology", Section 2.7, gives Hurewicz' proof of the theorem that a local (Hurewicz) fibration with respect to a numerable open cover of …
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7 votes

The complex $K$-theory of the Thom spectrum $MU$

You can learn about this, and more, in Part II of Adams' "Stable Homotopy and Generalised Homology" (1974), especially section 4, in the special case $E = KU$.
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4 votes

Homology of braid groups and loop spaces

Looping the fiber sequence $S^1 \to S^3 \to S^2$ gives $\Omega^2 S^2 \simeq \mathbb{Z} \times \Omega^2 S^3$. This is the group completion $\mathbb{Z} \times BB_\infty^+$ of $\coprod_{n\ge0} BB_n$, so …
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6 votes

Classifying the endofunctors of the category $\Delta$ of finite linear orders

See Edgewise subdivision and simple maps by Knut Berg (supervised by me), Generalized edgewise subdivisions by Katerina Velcheva (supervised by Clark Barwick) and the earlier MathOverflow question Wha …
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3 votes

Defining homotopy via endofunctors of a simplicial category

There is a problem with base points in your claim. If $X$ is discrete, then ${\rm sing} X_\bullet$ and ${\rm sing} X_\bullet \circ [+1]$ are the same, so every map from ${\rm sing} F_\bullet$ factors …
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3 votes

Numerator in the zeta values at negative odd integers

(Too long for a comment:) As A.S. commented, the absolute value of $\zeta(1-2k) = - B_{2k}/2k$ for $k\ge1$ is realized as twice the order of $K_{4k-2}(Z)$ divided by the order of $K_{4k-1}(Z)$, so for …
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8 votes
Accepted

$BP$-Adams Novikov Spectral Sequence or Homotopy groups of $S/3$

For $3$-primary homotopy of $S$ there is early work by Nakamura, Osamu Some differentials in the mod 3 Adams spectral sequence. Bull. Sci. Engrg. Div. Univ. Ryukyus Math. Natur. Sci. No. 19 (1975), 1– …
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4 votes

What is $TP(\mathbb{Z}_p)$?

The calculation of $\pi_* TP(\mathbb{F}_p) = \pi_* THH(\mathbb{F}_p)^{tS^1} = \pi_* \widehat{\mathbb{H}}(S^1, THH(\mathbb{F}_p))$ (the notation has changed over the years) was first published by Hesse …
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7 votes
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Generalization of Hopf invariant

The $E$-based Adams spectral sequence is the homotopy spectral sequence associated to the tower of spectra $\dots \to Y_2 \to Y_1 \to Y_0 = S$ with $Y_{s+1} \to Y_s \to E \wedge Y_s$ a homotopy fiber …
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