One of the most important spaces for the permanent exhibition of artists from the Minimalist generation — the Hallen für Neue Kunst (or Halls for New Art), in Schaffhausen, Switzerland — was forced to close last year, the victim of a protracted lawsuit that depleted its modest resources. But at least for a while, Europe’s loss will be New York’s gain. The Dia Art Foundation, whose focus on the artists of the 1960s and ’70s made it a kind of American sister to the Schaffhausen institution, announced that it would mount the first American survey in more than 20 years of the work of Robert Ryman, whose austere white-on-white paintings are among the most important of the postwar period and who long had a sizable body of work on display in Schaffhausen.