1 Transgression Sequence of a Fibration
F → E → B is a fibration of finite spaces and suppose that F and B are m-
and n-connective, respectively. If n > 0, Then there is a Serre spectral sequence
H
p
(B; H
q
(F ; Z)) ⇒ H
p+q
(E)
The r-th page, for r < m, of the spectral sequence features only one non-trivial
differential:
d
r
: H
n+r
(F ) → H
n+r−1
(F )
And after the r-th page, for r < m, the spectral sequence is constant in total
degree n + r. We have deduced
Proposition 1.0.1. There is an exact sequence
H
n+m−1
(E) → ... → H
n+r
(E) → H
n+r
(B)
d
r
→ H
n+r−1
(F ) → H
n+r
1
(E) → ...
for −n < r < m, where d
r
= 0 when r < 0.
Definition 1.0.1. The map d
r
is called the r-th transgression map (of the
fibration). We call the exact sequence of Proposition (1.0.1) the transgression
sequence of the underlying fibration.
1.1 Transgression for Loop Spaces
For an n-connective space X, with n > 1, we have transgression maps
d
r
: H
n+r
(X) → H
n+r−1
(ΩX)
arising from the path loop fibration ΩX → PX → X. PX is contractible, so
the transgression sequence implies that
d
r
: H
n+r
(X) → H
n+r−1
(ΩX)
is an isomorphism, for r < n.
1.2 Relation With The Boundary Map
Proposition 1.0.2. For r < m, the following diagram commutes
π
n+r
(B) π
n+r−1
(F )
H
n+r
(B) H
n+r
(E)
∂
d
r
1
Proof. d
r
([f]), where f : S
n+r
→ S
n+r−1
corresponds to chasing [f ] up the
double complex C(B) ⊗ C(F ).
d
r
[f] ...
d
2
([f])
˜
h[f]
∂h[f] [f]
But passing through the identification of C(E) with C(B) ⊗ C(F ), which is
implicit in the Serre Spectral sequence, the full diagram chase is equivalent to
a lift,
˜
[f], of [f] to C(E)
n+r
and we have d
r
= ∂[f], which by construction lies
in C(B)
n+r−1
. On the other hand, we could have lifted f to an n + r-cell of E,
and taken its boundary up to homotopy, and then applied the Hurewicz map.
These two constructions must have the same output, up to homotopy.
1.3 The co-Suspension Theorem
ϵ : ΣΩ → id is the co-unit of the suspension-loop adjunction.
Proposition 1.0.3 (co-Suspension). Let X be a connected pointed space.
1. If X is n-connective, with π
n
(X) Abelian, then ϵ : H
n+r
(ΣΩX)
n+r
→
H
n+r
(X) is an isomorphism for r < n.
2. If r < n then the following diagram commutes
H
n+r
(ΣΩX) H
n+r−1
(ΩX)
H
n+r
(X)
∂
∼
ϵ
∼
d
r
∼
(1)
Proof.
2