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Ivancevic_Applied-Diff-Geom

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670 <strong>Applied</strong> <strong>Diff</strong>erential <strong>Geom</strong>etry: A Modern IntroductionExplicitly,Letɛ(v) (v 1 ∧ · · · ∧ v k ) = v ∧ v 1 ∧ · · · ∧ v k .ι : V −→ Hom( Λ k V , Λ k−1 V )be the action of V on ΛV by interior product (or contraction), i.e., for allv ∈ V ,Explicitly,ι(v) (v 1 ∧ · · · ∧ v k ) =ι(v) : Λ k V −→ Λ k−1 Vw ↦−→ Q(v, w) .k∑(−1) i−1 Q(v, v i ) v 1 ∧ · · · ∧ ̂v i ∧ · · · ∧ v k .i=1The Clifford action of v ∈ V on w ∈ ΛV is given byFor any v, w in V , we havev · w = c(v) w = ɛ(v) w − ι(v) w.cɛ(v) ι(w) + ι(w) ɛ(v) = Q(v , w).The action c : V −→ End(ΛV ) extends to an action of the Cliffordalgebra C(V ) on ΛV .The symbol map σ : C(V ) −→ ΛV is defined by σ(a) = c(a) 1 ΛV, where1 ΛV∈ Λ 0 V is the identity in the exterior algebra ΛV .If 1 C(V )denotes the identity in C(V ), then σ(1 C (V )) is the identity1 End(ΛV )in End(ΛV ).The Clifford algebra C(V ) is isomorphic to the tensor algebra ΛV andis therefore a 2 dim V dimensional vector space with generators{(c 1 ) n1 (c 2 ) n2 . . . (c dim V) n dim V | (n1 , n 2 , . . . , n dim V) ∈ {0, 1} dim V }.If we consider C(V ) and ΛV as Z 2 −graded O(V )−modules, then σ andpreserve the Z 2 −graded and the O(V ) action. Hence they are isomorphismsof Z 2 −graded O(V )−modules.There is a natural increasing filtration∞⋃C 0 (V ) ⊆ C 1 (V ) ⊆ . . . ⊆ C k (V ) ⊆ . . . ⊆ C i (V ) = C(V ),i=0

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