A mathematical 'aventure', exploring an interlocked, layered design within the four poems of Cotton Nero A.x. Key structural elements are identified as mathematical metaphors for theological concepts; e.g. 490 as 'seventy times seven' alludes to forgiveness or 101 as a 'Pythagorean Comma' alludes to the Music of the Spheres. The author concludes from an analysis of the numerical literary technique and comparison with other medieval poetic mathematics that the four poems - Pearl, Patience, Purity & Sir Gawain and the Green Knight - are meant to form a rhetorical debate with each of the 'Four...