The “them” — the ghosts in the room — are David Gordon and Valda Setterfield, two of the most important artists to emerge from New York’s postmodern dance scene. It was in this Manhattan loft that they worked and lived for decades. (Gordon died in 2022 and Setterfield in 2023.) Now, if you knew them, what you feel even more than the raw spaciousness of the loft, a pillar-free treasure, is their absence.