ÖYVIND FAHLSTRÖM was, of course, the Swedish artist who immigrated to New York in 1961 and became known for work that was related to Pop art but had a political bent that made it marginal to the movement.

True enough. And yet this retrospective, the most comprehensive ever mounted of Fahlström's work, showed that almost every word in that sentence stands in need of questioning—starting with the seemingly straightforward matter of his relation to Pop art. His pair of vacuum-formed plastic signs, ESSO-LSD, 1967, are as characteristic of the period as better-known icons like Robert Indiana's Love