 The ancients stated that there are three kinds of geometrical problems, and that some are called plane, others solid, and others line-like; and those that can be solved by straight lines and the circumference of a circle are rightly called plane because the lines by means of which these problems are solved have their origin in the plane. But such problems that must be solved by assuming one or more conic sections in the construction, are called solid because for their construction it is necessary to use the surfaces of solid figures, namely cones. There remains a third kind that is called line-like. For in their construction other lines than the ones just mentioned are assumed, having an inconstant and changeable origin, such as spirals, and the curves that the Greeks call tetragonizousas [“square-making”], and which we call “quandrantes,” and conchoids, and cissoids, which have many amazing properties (Pappus 1588, III, §7; translation from Bos 2001, 38).