“The first and most important thing is to remain free,” stated Hans Hartung, one of the key figures of the Art Informel movement, “free in each line you undertake, in your ideas and in your political action, in your moral conduct.” He added, “The artist especially must remain free from all outer restraints.” This was particularly challenging for Hartung, who lived from 1904 to 1989, and who escaped fascist Germany only to be imprisoned later by the Gestapo for his “immoral artwork.” Reopening after renovation, the Musée d’Art Moderne shows 300 of Hartung’s works, in which experimental slashes and scribbles read like a rebuke to forces that stifle. —E.C.