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A note on Witt rings of 2-fold full rings. (English) Zbl 0587.13004
The main theorem is that when R and S are 2-fold full, the Witt rings W(R) and W(S) are isomorphic if and only if $$W(R)/I(R)^ 3$$ and $$W(S)/I(S)^ 3$$ are isomorphic, where I(R) and I(S) are the fundamental ideals of W(R) and W(S) respectively. The analogous results for the cases when R and S are fields, or semi-local rings with 2 invertible, are due to D. K. Harrison; cf. J. K. Arason and A. Pfister [Invent. Math. 12, 173-176 (1971; Zbl 0212.373)] and K. I. Mandelberg [Can. J. Math. 27, 513-527 (1975; Zbl 0273.13017)].
Reviewer: C.Small

##### MSC:
 13C05 Structure, classification theorems for modules and ideals in commutative rings 11E16 General binary quadratic forms