[https://edition.cnn.com/style/article/yves-klein-invisible-art-sothebys-auction/index.html](https://edition.cnn.com/style/article/yves-klein-invisible-art-sothebys-auction/index.html) >"A handwritten receipt, which represents ownership of empty space imagined by conceptual artist Yves Klein in the 1950s, fetched $1.16 million at a Paris auction."