Does everything in the world obey a mathematical logic, can everything be calculated? In our present age of probability, some would say the answer is a straightforward yes, inevitably prompting the question: Even art? Yes, even art, or so the defenders of Concrete Art would respond, a twentieth-century movement that took abstraction as a focus on the "idea of art itself" (W. Kandinsky) to the next level. The act of painting was now to be subject to preconceived organizing principles as though they were laws of nature. One prominent exponent of the genre was Aurélie Nemours (1910-2005), who had a penchant for the square; her credo was that it needed to "rule space." That is why the equilateral quadrangle is the defining shape in this catalog, which brings Nemours' oeuvre into focus. Her iconic position is flanked by works by seventeen others that similarly grapple with the square, including pictures and sculptures with square basic forms, grids, or canvases. All these works derive their force from the stern authority of the square: only when art constrains its means can it bring its full potential to bear.