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D* extension property without hyperbolicity

1998, Indiana University Mathematics Journal

Abstract

We present an example of a complex manifold X-in fact, a pseudoconvex open set in C 2-such that X is not Kobayashi-hyperbolic, but any holomorphic map from the punctured unit disk to X extends to a map from the whole unit disk to X. 0. Introduction. Let X be a complex manifold. We say that X has the D *-extension property (D *-EP) iff for any holomorphic map f from D * = {z ∈ C : 0 < |z| < 1} to X, there exists a mapf ∈ Hol(D,X) (where D = {z ∈ C : |z| < 1}) such thatf | D * = f. Kwack [4] and Thai [8] proved that in the case where X is compact, then the D *-EP is equivalent to hyperbolicity in the sense of Kobayashi, as well as in the sense of Brody (see precise definitions below). If X is not assumed to be compact, X = D * , f (z) = z provides an immediate example of a hyperbolic (indeed, complete hyperbolic) manifold which does not have the D *-EP. But if X has the D *-EP, then it must be Brody-hyperbolic [8]. The purpose of this note is to give an example of a complex manifold X (in fact, an open set in C 2) which has the D *-EP but is not Kobayashihyperbolic. Note that our example is pseudo-convex, and in fact any Riemann domain spread over C n having the D *-EP must be pseudo-convex. Whether an arbitrary complex manifold X having the D *-EP is also pseudoconvex, or verifies the Kontinuitätssatz, is an interesting open problem.