Writing ten years after Barbara Hepworth’s Single Form was erected outside the United Nations building in New York, the critic Lawrence Alloway wondered whether it succeeded as a public sculpture. He decided that its meaning was too hard to grasp: in the end, “it is a Barbara Hepworth and that is that”. Being a Barbara Hepworth was enough in 1974, when she was one of the world’s most famous living sculptors, but is it still enough for a contemporary audience that remembers her chiefly as the inventor of the sculpture with the hole? A major retrospective at Tate Britain is finding out. To those stuck at the “Polo” stage with Hepworth, the first room of “Barbara Hepworth: Sculpture for a Modern World” (until 25 October) will be a revelation. A