Published online by Cambridge University Press: 24 October 2008
Let X be an affine real algebraic variety, i.e., up to biregular isomorphism an algebraic subset of ℝn. (For definitions and notions of real algebraic geometry we refer the reader to the book [6].) Let denote the ring of regular functions on X ([6], chapter 3). (If X is an algebraic subset of ℝn then
is comprised of all functions of the form f/g, where g, f: X → ℝ are polynomial functions with g−1(O) = Ø.) In this paper, assuming that X is compact, non-singular, and that dim X ≤ 3, we compute the Grothendieck group
of projective modules over
(cf. Section 1), and the Grothendieck group
and the Witt group
of symplectic spaces over
(cf. Section 2), in terms of the algebraic cohomology groups
and
generated by the cohomology classes associated with the algebraic subvarieties of X. We also relate the group
to the Grothendieck group KO(X) of continuous real vector bundles over X, and the groups
and
to the Grothendieck group K(X) of continuous complex vector bundles over X.