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Proper cycles of indefinite quadratic forms and their right neighbors

Ahmet Tekcan (2007)

Applications of Mathematics

In this paper we consider proper cycles of indefinite integral quadratic forms F = ( a , b , c ) with discriminant Δ . We prove that the proper cycles of F can be obtained using their consecutive right neighbors R i ( F ) for i 0 . We also derive explicit relations in the cycle and proper cycle of F when the length l of the cycle of F is odd, using the transformations τ ( F ) = ( - a , b , - c ) and χ ( F ) = ( - c , b , - a ) .

Purity of level m stratifications

Marc-Hubert Nicole, Adrian Vasiu, Torsten Wedhorn (2010)

Annales scientifiques de l'École Normale Supérieure

Let k be a field of characteristic p > 0 . Let D m be a BT m over k (i.e., an m -truncated Barsotti–Tate group over k ). Let S be a k -scheme and let X be a BT m over S . Let S D m ( X ) be the subscheme of S which describes the locus where X is locally for the fppf topology isomorphic to D m . If p 5 , we show that S D m ( X ) is pure in S , i.e. the immersion S D m ( X ) S is affine. For p { 2 , 3 } , we prove purity if D m satisfies a certain technical property depending only on its p -torsion D m [ p ] . For p 5 , we apply the developed techniques to show that all level m ...

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