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Let B be a 2-dimensional ring with an action of a group G. The combinatorial
data associated with the desingularization of the ring of invariants BG
produces a symmetric semi-definite negative integer quadratic form, and properties
of this form will be described in the wild case, that is, when the residual characteristic
of B is not coprime to the order of G. This is intended to be a friendly
introduction to this subject, and motivations and examples will be included.
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