Choreographer Trisha Brown, who died in March, created revolutionary pieces that explored vertical space and the relationship of the body to gravity. She equipped her dancers with ropes and harnesses to scale walls, and, in works like “Roof Piece,” had them perform in synchrony on neighboring Manhattan rooftops, using a vocabulary of ripples, ricochets, and other elastic movements that defied traditional dance notation. In this illuminating documentary, we watch as the Paris Opera Ballet learns her seminal 1979 piece “Glacial Decoy.” But how would the classical dancers master a language so antithetical to everything they knew? The task of coaching them fell to two longtime Trisha Brown collaborators: Lisa Kraus, who helped create “Glacial Decoy,” and Carolyn Lucas. “What I told them to do,” Kraus recalls, “was exactly the opposite of what their training told them. So we did a lot of undoing.” In the Steps of Trisha Brown takes us behind the scenes as the women instruct and inspire their charges, coaxing them into a performance that is a joy to behold.