In her powerful new documentary “13th,” filmmaker Ava DuVernay (Selma) explores the history of racial inequality in the United States, focusing on the fact that the nation's prisons are disproportionately filled with African-Americans. Tonight’s free screening at the DC LaborFest’s Bread and Roses series at the Takoma Park Busboys (see Calendar for details), will be introduced by Carmen Berkley, Civil, Human and Women's Rights Director at the AFL-CIO. “You feel that you're seeing an essential dimension of America with new vision,” says Variety film critic Owen Gleiberman. “That's what a cathartically clear-eyed work of documentary art can do.” View the trailer here.