By J. M. Aroca, R. Buchweitz, M. Giusti, M. Merle

ISBN-10: 3540119698

ISBN-13: 9783540119692

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**Extra info for Algebraic Geometry, la Rabida, Spain 1981: Proceedings**

**Example text**

Where Γ is a lifted curve and f denotes df /dx. It follows that |Γ, Γx , . . x | = |Γ, Γy , . . y |(f )n(n+1)/2 , and, therefore, the Wronski determinant W (x) is a tensor density of degree n(n + 1)/2, that is, an element of Fn(n+1)/2 . 5). 4) are −n/2-densities. 3) it follows that the kernel of the operator A consists of −n/2-densities. It remains to note that the kernel uniquely defines the corresponding operator. The brevity of the proof might be misleading. 3 by a direct computation. g.

We define a canonical PGL(2, R)-isomorphism between this space and the space of tensor densities on S 1 . We apply this isomorphism to construct projective differential invariants of non-degenerate curves in RPn . Space of symbols There is a natural filtration 0 1 k Dλ,µ (S 1 ) ⊂ Dλ,µ (S 1 ) ⊂ · · · ⊂ Dλ,µ (S 1 ) ⊂ · · · The corresponding graded Diff(S 1 )-module Sλ,µ (S 1 ) = gr (Dλ,µ (S 1 )) is called the module of symbols of differential operators. k (S 1 )/D k−1 (S 1 ) is isomorphic to the module of The quotient-module Dλ,µ λ,µ tensor densities Fµ−λ−k (S 1 ); the isomorphism is provided by the principal 46 CHAPTER 2.

Indeed, fix a parameter value x = x 0 , (j) and choose a special basis φ0 , . . , φn ∈ U such that φi (x0 ) = 0 for all (i) i = j; i, j = 0, . . , n, and φi (x0 ) = 1 for all i. Let ψi ∈ V be the basis in V defined similarly. In these bases, the matrix of B(φ, ψ)(x 0 ) is triangular with the diagonal elements equal to ±1. ˜ The pairing B allows us to identify U ∗ with V . 6). Let Γ(x) ⊂ V be a similar curve corresponding to A ∗ . We want to show that these two curves are dual with respect to the pairing B, that is, ˜ (i) (x0 ), Γ(x0 )) = 0, i = 0, .

### Algebraic Geometry, la Rabida, Spain 1981: Proceedings by J. M. Aroca, R. Buchweitz, M. Giusti, M. Merle

by Ronald

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