The geometry of the Weddle manifold ๐_{๐}
Arthur B. Coble ยท Bulletin of the American Mathematical Society ยท 1935
Cremona transformations are characterized by the property that they are completely defined to within collineations at most by a finite number of F'-points, the existence of other FAoci, jP-curves, .F-surfaces, etc., being a necessary consequence of the existence of these F-points.Returning to 5 2 we take 2+3 points, pu p 2 , โข โข โข , pz = P& 2 , and denote by In that involution I yz which interchanges pi and p 2 and which has .F-points at pz, pยฑ, p&.Then the ten involutions I%h (^i i-1ยป ' ' * ยป 5; ifรฉj), generate a finite abelian group of order 2 4 and type (1,1,1,1) whose elements multiply according to the following rules: