O Teorema de Stokes em Variedades - Fernando UFMS/CPAq
O Teorema de Stokes em Variedades - Fernando UFMS/CPAq
O Teorema de Stokes em Variedades - Fernando UFMS/CPAq
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2.1 Formas Alternadas 36<br />
então<br />
=<br />
<br />
1<br />
(k + l)!<br />
sgn(σ0) ·<br />
<br />
σ∈G·σ0<br />
1<br />
(k + l)!<br />
sgn(σ) · S(vσ(1), · · · , vσ(k)) · T (vσ(k+1), · · · , vσ(k+l)) =<br />
<br />
σ ′ ∈G<br />
sgn(σ ′ ) · S(wσ ′ (1), · · · , wσ ′ (k))<br />
= Alt(S) · T (wk+1, · · · , wk+l) = 0.<br />
<br />
· T (wk+1, · · · , wk+l) =<br />
A <strong>de</strong>montração <strong>de</strong> que Alt(T ⊗ S) = 0 se faz <strong>de</strong> forma similar.<br />
<strong>Teor<strong>em</strong>a</strong> 2.1.7. Sejam ω ∈ Λ k (V ), η ∈ Λ l (V ) e θ ∈ Λ m (V ), então Alt(Alt(ω ⊗ η) ⊗ θ) =<br />
Alt(ω ⊗ η ⊗ θ) = Alt(ω ⊗ Alt(η ⊗ θ)).<br />
D<strong>em</strong>onstração. Observe que<br />
logo, pelo teor<strong>em</strong>a anterior,<br />
Então<br />
Alt(Alt(η ⊗ θ) − η ⊗ θ) = Alt(η ⊗ θ) − Alt(η ⊗ θ) = 0,<br />
0 = Alt(ω[Alt(η ⊗ θ) − η ⊗ θ]) =<br />
= Alt(ω ⊗ Alt(η ⊗ θ)) − Alt(ω ⊗ η ⊗ θ).<br />
Alt(Alt(ω ⊗ η) ⊗ θ) = Alt(ω ⊗ η ⊗ θ).<br />
O caso Alt(ω ⊗ Alt(η ⊗ θ)) = Alt(ω ⊗ η ⊗ θ) se prova <strong>de</strong> forma similar.<br />
<strong>Teor<strong>em</strong>a</strong> 2.1.8. Sejam ω ∈ Λ k (V ), η ∈ Λ l (V ) e θ ∈ Λ m (V ), então (ω ∧ η) ∧ θ =<br />
ω ∧ (η ∧ θ) = (k+l+m)!<br />
Alt(ω ⊗ η ⊗ θ).<br />
k!l!m!<br />
D<strong>em</strong>onstração.<br />
= (k + l + m)!<br />
(k + l)!m!<br />
(ω ∧ η) ∧ θ =<br />
· (k + l)!<br />
k!l!<br />
(k + l + m)!<br />
Alt((ω ∧ η) ⊗ θ) =<br />
(k + l)!m!<br />
(k + l + m)!<br />
Alt(ω ⊗ η ⊗ θ) = Alt(ω ⊗ η ⊗ θ).<br />
k!l!m!<br />
De fato, o que acabamos <strong>de</strong> mostrar é que vale a associativida<strong>de</strong><br />
ω ∧ (η ∧ θ) = (ω ∧ η) ∧ θ = ω ∧ η ∧ θ. (2.1)