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Conformally Invariant Variational Problems. - SAM

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where  and ˆB are arbitrary functions in L ∞ ∩ W 1,2 and in<br />

W 1,2 respectively. An analogousversion 27 of theorem VII.1 with<br />

NeumanboundaryconditionsinplaceofDirichletconditions,we<br />

deduce that the unique solution (Ã,B) of (VIII.36) satisfies the<br />

estimates<br />

∫<br />

∫<br />

|∇Ã|2 +‖Ã−Id m‖ 2 ∞ ≤ C<br />

D<br />

∫D |∇Â|2 |∇ξ| 2<br />

2 2 D<br />

∫<br />

2<br />

+C |∇ˆB|<br />

∫D 2 |∇P| 2 ,<br />

2 D 2 (VIII.38)<br />

and<br />

∫ ∫<br />

|∇(˜B −B 0 )| 2 ≤ C ‖Â−Id m‖ 2 ∞ |∇ξ| 2<br />

D 2 D<br />

∫<br />

2<br />

+C<br />

∫D |∇Â|2 |∇P| 2 ,<br />

2 D 2<br />

where B 0 is the solution in W 1,2 of<br />

⎧<br />

⎨ ∆B 0 = −div(∇ξ P −1 ) in D 2<br />

⎩<br />

Hence, if<br />

(VIII.39)<br />

B 0 = 0 on ∂D 2 (VIII.40)<br />

∫<br />

D 2 |∇P| 2 +|∇ξ| 2<br />

issufficientlysmall(thiscanalwaysbearrangedowingto(VIII.35)<br />

and the hypothesis (VIII.25)), then a standard fixed point argument<br />

in the space ( L ∞ ∩W 1,2 (D 2 ,M m (R)) ) ×W 1,2 (D 2 ,M m (R))<br />

27 whose proof is left as an exercise.<br />

90

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