The mathematician Gerolamo Cardano discusses the problem of the wheel in his 1570 "Opus novum de proportionibus numerorum", taking issue with the presumption of the analysis of the problem in terms of motion. Mersenne further discussed the wheel in his 1623 "Quaestiones Celeberrimae in Genesim", where he suggests that the problem can be analysed by a process of expansion and contraction of the two circles. But Mersenne remained unsatisfied with his understanding, writing,Indeed I have never been able to discover, and I do not think any one else has been able to discover whether the smaller circle touches the same point twice, or proceeds by leaps and sliding.