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The purpose of this article is towards systematically characterizing (holomorphic) retracts of domains of holomorphy; to begin with, bounded balanced pseudoconvex domains $B \subset \mathbb{C}^N$. Specifically, we show that every retract of $B$ passing through its center (origin), is the graph of a holomorphic map over a linear subspace of $B$. As for retracts not passing through origin, we obtain the following result: if $B$ is a strictly convex ball and $\rho$ any holomorphic retraction map on $B$ which is submersive at its center, then $Z=\rho(B)$ is the graph of a holomorphic map over a linear subspace of $B$. To deal with a case when $\partial B$ may fail to have sufficiently many extreme points, we consider products of strictly convex balls, with respect to various norms and obtain a complete description of retracts passing through its center. This can be applied to solve a special case of the union problem with a degeneracy, namely: to characterize those Kobayashi corank one complex manifolds $M$ which can be expressed as an increasing union of submanifolds which are biholomorphic to a prescribed homogeneous bounded balanced domain. Results about non-existence of retracts of each possible dimension is established for the simplest non-convex but pseudoconvex domain: the `$\ell^q$-ball' for $0Comment: An erroneous statement in the introduction to the effect that a taut convex domain is biholomorphic to a bounded {\it convex} domain has been set right alongwith other non-major errors. Exposition has been improved to remove sloppiness, particularly in the last section. Most of these changes have been highlighted, in blue; specifically, these appear in pages 9, 11, 63 and 83 |
