Detection by regular schemes in degree two

Abstract

Using Lipman's results on resolution of two-dimensional singularities, we provide a form of resolution of singularities in codimension two for reduced quasi-excellent schemes. We deduce that operations of degree less than two on algebraic cycles are characterised by their values on classes of regular schemes. We provide several applications of this "detection principle", when the base is an arbitrary regular excellent scheme: integrality of the Chern character in codimension less than three, existence of weak forms of the second and third Steenrod squares, Adem relation for the first Steenrod square, commutativity and Poincaré duality for bivariant Chow groups in small degrees. We also provide an application to the possible values of the Witt indices of non-degenerate quadratic forms in characteristic two.

final version

References in corpus (2)

• Desingularization of quasi-excellent schemes in characteristic zero
• On the first Steenrod square for Chow groups

Cited by in corpus (4)

• Hoffmann's conjecture for totally singular forms of prime degree
• Involutions of varieties and Rost's degree formula
• Motivic Steenrod operations in characteristic $p$
• Connective K-theory and Adams operations