# Igusa-Clebsch invariants

I am looking for a good reference for definitions and basic properties of the Igusa-Clebsch invariants for curves of genus $2$ (especially, but not only, in positive characteristic).

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Edited only to add the reference-request tag. Note that except in characteristic 2 the invariants of a genus-2 curve are also the invariants of a binary sextic (= homogeneous sextic in two variables up to linear coordinate changes). –  Noam D. Elkies Jun 14 '12 at 2:54
Have you read Igusa's original paper? I think it's pretty readable except it's not written in scheme language. –  Dan Petersen Jun 14 '12 at 8:45
Which paper of Igusa should I read? –  averageman Jun 14 '12 at 14:30
Sorry, I mean "Arithmetic Variety of Moduli for Genus Two". –  Dan Petersen Jun 14 '12 at 18:41