High Quality Content by WIKIPEDIA articles! In mathematics, an arithmetic group (arithmetic subgroup) in a linear algebraic group G defined over a number field K is a subgroup of G(K) that is commensurable with G(O), where O is the ring of integers of K. Here two subgroups A and B of a group are commensurable when their intersection has finite index in each of them. It can be shown that this condition depends only on G, not on a given matrix representation of G. Examples of arithmetic groups include therefore the groups GLn(Z). The idea of arithmetic group is closely related to that of lattice in a Lie group. Lattices in that sense tend to be arithmetic, except in well-defined circumstances. The exact relationship of the two concepts was established by the work of Margulis on superrigidity. The general theory of arithmetic groups was developed by Armand Borel and Harish-Chandra, the description of their fundamental domains was in classical terms the reduction theory of algebraic forms.
A detailed treatment of the geometric aspects of discrete groups was carried out by Raghunathan in his book "Discrete subgroups of Lie Groups" which appeared in 1972. In particular he covered the theory of lattices in nilpotent and solvable Lie groups, results of Mal'cev and Mostow, and proved the Borel density theorem and local rigidity theorem ofSelberg-Weil. He also included some results on unipotent elements of discrete subgroups as well as on the structure of fundamental domains. The chapters concerning discrete subgroups of semi simple Lie groups are essentially concerned with results which were obtained in the 1960's. The present book is devoted to lattices, i.e. discrete subgroups of finite covolume, in semi-simple Lie groups. By "Lie groups" we not only mean real Lie groups, but also the sets of k-rational points of algebraic groups over local fields k and their direct products. Our results can be applied to the theory of algebraic groups over global fields. For example, we prove what is in some sense the best possible classification of "abstract" homomorphisms of semi-simple algebraic group over global fields.
Metric theory has undergone a dramatic phase transition in the last decades when its focus moved from the foundations of real analysis to Riemannian geometry and algebraic topology, to the theory of infinite groups and probability theory.The new wave began with seminal papers by Svarc and Milnor on the growth of groups and the spectacular proof of the rigidity of lattices by Mostow. This progress was followed by the creation of the asymptotic metric theory of infinite groups by Gromov.The structural metric approach to the Riemannian category, tracing back to Cheeger's thesis, pivots around the notion of the Gromov Hausdorff distance between Riemannian manifolds. This distance organizes Riemannian manifolds of all possible topological types into a single connected moduli space, where convergence allows the collapse of dimension with unexpectedly rich geometry, as revealed in the work of Cheeger, Fukaya, Gromov and Perelman. Also, Gromov found metric structure within homotopy theory and thus introduced new invariants controlling combinatorial complexity of maps and spaces, such as the simplicial volume, which is responsible for degrees of maps between manifolds. During the same period, Banach spaces and probability theory underwent a geometric metamorphosis, stimulated by the Levy Milman concentration phenomenon, encompassing the law of large numbers for metric spaces with measures and dimensions going to infinity.The first stages of the new developments were presented in Gromov's course in Paris, which turned into the famous "Green Book" by Lafontaine and Pansu (1979). The present English translation of that work has been enriched and expanded with new material to reflect recent progress. Additionally, four appendices by Gromov on Levy's inequality, by Pansu on "quasiconvex" domains, by Katz on systoles of Riemannian manifolds, and by Semmes overviewing analysis on metric spaces with measures as well as an extensive bibliography and index round out this unique and beautiful book.
High Quality Content by WIKIPEDIA articles! In domain theory, a branch of mathematics and computer science, a Scott information system is a primitive kind of logical deductive system often used as an alternative way of presenting Scott domains. In the mathematical fields of order and domain theory, a Scott domain is an algebraic, bounded complete cpo. It has been named in honour of Dana S. Scott, who was the first to study these structures at the advent of domain theory. Scott domains are very closely related to algebraic lattices, being different only in possibly lacking a greatest element.
High Quality Content by WIKIPEDIA articles! In the mathematical fields of order and domain theory, a Scott domain is an algebraic, bounded complete cpo. It has been named in honour of Dana S. Scott, who was the first to study these structures at the advent of domain theory. Scott domains are very closely related to algebraic lattices, being different only in possibly lacking a greatest element.Since the empty set certainly has some upper bound, we can conclude the existence of a least element (the supremum of the empty set) from bounded completeness. Also note that, while the term "Scott domain" is widely used with this definition, the term "domain" does not have such a general meaning: it may be used to refer to many structures in domain theory and is usually explained before it is used.