Yvonne Rainer, 87, photographed in Fort Tryon Park.

“In 1966, Yvonne Rainer presented ‘Trio A,’ her celebrated solo that emphasized movement over expression. By stripping dance of narrative, of emotion and even of the dancer’s gaze — there is no looking at the audience — the steps could shine. And those steps, delivered with the same temperament no matter how simple or difficult, were the dance. What did Rainer banish? Affectation. In another iteration of ‘Trio A,’ in 1970, the work expanded to six dancers, including Rainer, who performed nude with American flags tied around their necks like halter tops, at the People’s Flag Show at Judson Memorial Church in New York. The event was a response to the prosecution of the gallery owner Stephen Radich for showing work that desecrated the flag. Censorship, the Vietnam War — these were issues of the day. Now at 87, with 61 years…