theorem
ProbabilityTheory.Copula.RankRegion.RhoTau.inverse_coefficients
{n : ℕ}
(π : Equiv.Perm (Fin n))
(u : Fin n → ℝ)
:
(permutationSigns (Equiv.symm π)).a (u ∘ ⇑(Equiv.symm π)) = (permutationSigns π).a u ∧ (permutationSigns (Equiv.symm π)).b (u ∘ ⇑(Equiv.symm π)) = (permutationSigns π).b u