A champagne subdomain of a connected open set in , , is obtained by omitting pairwise disjoint closed balls , , the bubbles, where is an infinite, locally finite set in . The union of these balls may be unavoidable, that is, Brownian motion, starting in and killed when leaving? , may hit? almost surely or, equivalently, may have harmonic measure 1 for .
Recent publications by Gardiner and Ghergu () and by Pres () give rather sharp answers to the question of how small such a set may be, when ?is the unit ball.
In this paper, using a totally different approach, optimal results are obtained, which hold also for arbitrary connected open sets? .