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Then<br />
ind∂A = ind∂A1 + ind∂A1.<br />
The proof is analogous to the proof of Theorem 3.2.12 in [Sch95], and we omit it. When there<br />
are no jumps, that is S = ∅ and V = (V ), V ′ = (V ′ ), Theorem 5.11 shows that the index of the<br />
operator<br />
is<br />
∂A : X 1,p<br />
∅,(V ),(V ′ ) (Σ,�n ) = W 1,p<br />
N ∗ V,N ∗ V ′(Σ,�n ) → L p (Σ,�n ) = X p<br />
∅ (Σ,�n )<br />
In the general case, Proposition 5.19 shows that<br />
ind∂A = µ(Φ − N ∗ V, N ∗ V ′ ) − µ(Φ + N ∗ V, N ∗ V ′ ).<br />
= µ(Φ − N ∗ V0, N ∗ V ′<br />
0 ) − µ(Φ+ N ∗ Vk, N ∗ V ′<br />
where the correction term c satisfies the additivity formula<br />
ind (∂A : X 1,p<br />
S ,V ,V ′(Σ,�n ) → X p<br />
S (Σ,�n ))<br />
k ′) + c(V0, . . .,Vk; V ′<br />
0<br />
, . . .,V ′<br />
k ′),<br />
c(V0, . . . , Vk+h; V ′<br />
0, . . .,V ′<br />
k ′ +h ′) = c(V0, . . . , Vk; V ′<br />
0, . . . , V ′<br />
k ′) + c(Vk, . . .,Vk+h; V ′ ′<br />
k ′, . . .,V<br />
k ′ +h ′).<br />
(112)<br />
(113)<br />
Since the Maslov index is in general a half-integer, and since we have not proved that the cokernel<br />
of ∂A is finite dimensional, the correction term c takes values in (1/2)�∪{−∞}. Actually, the<br />
analysis of this section shows that c is always finite, proving that ∂A is Fredholm.<br />
Clearly, we have the following direct sum formula<br />
c(V0 ⊕ W0, . . . , Vk ⊕ Wk; V ′<br />
0 ⊕ W ′ ′<br />
0 , . . .,V k ′ ⊕ W ′ k ′)<br />
= c(V0, . . . , Vk; V ′<br />
0, . . .,V ′<br />
k ′) + c(W0, . . .,Wk; W ′ 0, . . . , W ′ k ′).<br />
Note also that the index formula of Theorem 5.11 produces a correction term of the form<br />
(114)<br />
c(λ; ν) = µ(λ, ν), (115)<br />
where λ and ν are asymptotically constant paths of Lagrangian subspaces on�n . The Liouville<br />
type results of the previous section imply that<br />
Indeed, by Proposition 5.17 the operator<br />
c((0),Ên ;Ên ) = − n<br />
2 = c(Ên , (0);Ên ). (116)<br />
∂αI : X 1,p<br />
{0},((0),Ên ),(Ên ) (Σ,�n ) → X p<br />
{0} (Σ,�n )<br />
is an isomorphism if 0 < α < π/2. By (80), the Maslov index of the path e iαtÊn , t ∈ [0, 1], with<br />
respect toÊn is −n/2. On the other hand, the Maslov index of the path e iαt iÊn , t ∈ [0, 1], with<br />
respect toÊn is 0 because the intersection is (0) for every t ∈ [0, 1]. Inserting the information<br />
about the Fredholm and the Maslov index in (112), we find<br />
0 = ind∂αI = n<br />
2 + c((0),Ên ; (0)),<br />
which implies the first identity in (116). The second one is proved in the same way by using<br />
Proposition 5.18.<br />
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