I labirinti di Saul Steinberg

244-247 Saul

Family Planning Perspectives In 1996, as well, the Food and Drug Administration (FDA) took significant steps toward approving the use of medical (nonsurgical) abortion in the United States, essentially by “preapproving” the use of mifepristone, popularly known as RU 486, as an abortifacient; final approval is pending information on manufacturing and labeling. In addition, FDA cleared the way fo...

Aaron Abrams and Saul Schleimer

J. Hempel in [6] showed that the set of distances of the Heegaard splittings (S,V , hn(V)) is unbounded, as long as the stable and unstable laminations of h avoid the closure of V ⊂ PML(S). Here h is a pseudo-Anosov homeomorphism of a surface S while V is the set of isotopy classes of simple closed curves in S bounding essential disks in a fixed handlebody. With the same hypothesis we show that...

The Steinberg Representation

Introduction. Group representations occupy a sort of middle ground between abstract groups and transformation groups, i.e., groups acting in concrete ways as permutations of sets, homeomorphisms of topological spaces, diffeomorphisms of manifolds, etc. The requirement that the elements of a group act as linear operators on a vector space limits somewhat the complexity of the action without sacr...

Steinberg groups as amalgams

For any root system and any commutative ring, we give a relatively simple presentation of a group related to its Steinberg group St. This includes the case of infinite root systems used in Kac–Moody theory, for which the Steinberg group was defined by Tits and Morita–Rehmann. In most cases, our group equals St, giving a presentation with many advantages over the usual presentation of St. This e...

The Steinberg Wiring Problem