Naturality of the explicit low-degree cup products in compatible pairs #
A compatible pair (φ : H →ₜ* G, f : M →+ M') in the sense of
TauCeti/RepresentationTheory/Homological/ContCohomology/ExplicitFunctoriality.lean pulls a cup
product back to a cup product as soon as the two pairings are intertwined by the three coefficient
maps, f_P (μ m x) = μ' (f_M m) (f_N x):
(φ, f_P)^* (x ⌣_μ y) = (φ, f_M)^* x ⌣_{μ'} (φ, f_N)^* y.
Each of the six shapes (p, q) with p + q ≤ 2 gets one such theorem.
Main statements #
TauCeti.ContCohomology.explicitMap0_explicitCup00,explicitMap1_explicitCup01,explicitMap1_explicitCup10,explicitMap2_explicitCup02,explicitMap2_explicitCup20andexplicitMap2_explicitCup11: naturality in compatible pairs, one theorem per shape.TauCeti.ContCohomology.explicitCoeff0_explicitCup00,explicitCoeff1_explicitCup01,explicitCoeff1_explicitCup10,explicitCoeff2_explicitCup02,explicitCoeff2_explicitCup20andexplicitCoeff2_explicitCup11: naturality in the pairing, the instance at the pair(id, f), deduced from the general theorems throughTauCeti.ContCohomology.explicitCoeff1_eq_explicitMap1and its siblings.
Implementation notes #
The other named instance, the pair (S ↪ G, id), is compatibility with restriction; it is
deduced from these theorems in
TauCeti/RepresentationTheory/Homological/ContCohomology/Cup/Restriction.lean, where the
statements are simp lemmas.
References #
- J. Neukirch, A. Schmidt, K. Wingberg, Cohomology of Number Fields, 2nd ed., (1.4.2): naturality of the cup product in the coefficients.
Naturality of the (0,0) cup product in compatible pairs. In degree zero the cup product
is the pairing, so the statement is the intertwining hypothesis read on invariant elements.
Naturality of the (0,1) cup product in compatible pairs.
Naturality of the (1,0) cup product in compatible pairs.
Naturality of the (0,2) cup product in compatible pairs.
Naturality of the (2,0) cup product in compatible pairs.
Naturality of the (1,1) cup product in compatible pairs. This is the only shape in
which neither factor is invariant, so the cup is not a coefficient map.
The coefficient-map instances of the six naturality theorems, NSW (1.4.2): the compatible pair
is (id, f), the group does not move, and the intertwining hypothesis is naturality of the cup
product in the pairing.
Naturality of the (0,0) cup product in the coefficient maps (NSW (1.4.2)).
Naturality of the (0,1) cup product in the coefficient maps (NSW (1.4.2)).
Naturality of the (1,0) cup product in the coefficient maps (NSW (1.4.2)).
Naturality of the (0,2) cup product in the coefficient maps (NSW (1.4.2)).
Naturality of the (2,0) cup product in the coefficient maps (NSW (1.4.2)).
Naturality of the (1,1) cup product in the coefficient maps (NSW (1.4.2)).