Almgren's Big Regularity Paper, Q-valued Functions Minimizing Dirichlet's Integral And The Regularit Q-Valued Functions Minimizing Dirichlet's Integral and the Regularity of Area-Minimizing Rectifiable Currents up to Codimension 2

The Steinberg relations are the commutator relations which hold between elementary matrices in a special linear group. This text generalizes these sorts of relations. To encode these relations one needs a ring and a so-called linkage graph which specifies exactly which commutator relations hold. The groups obtained here, called linkage groups, have an enormous number of interesting images, finite and infinite. Among these images are, for example, 25 of the 26 finite sporadic simple groups. The book deals with the structure and classification of linkage groups. Part of the work involves theoretical group combinatorics and the other part involves computer calculations to study the linkage structure of various interesting groups. The book will be of value to researchers and graduate students in combinatorial and computational group theory Fred Almgren exploited the excess method for proving regularity theorems in the calculus of variations. His techniques yielded Hölder continuous differentiability except for a small closed singular set. In the sixties and seventies Almgren refined and generalized his methods. Between 1974 and 1984 he wrote a 1,700-page proof that was his most ambitious development of his ground-breaking ideas. Originally, this monograph was available only as a three-volume work of limited circulation. The entire text is faithfully reproduced here.This book gives a complete proof of the interior regularity of an area-minimizing rectifiable current up to Hausdorff codimension 2. The argument uses the theory of Q-valued functions, which is developed in detail. For example, this work shows how first variation estimates from squash and squeeze deformations yield a monotonicity theorem for the normalized frequency of oscillation of a Q-valued function that minimizes a generalized Dirichlet integral. The principal features of the book include an extension theorem analogous to Kirszbraun's theorem and theorems on the approximation in mass of nearly flat mass-minimizing rectifiable currents by graphs and images of Lipschitz Q-valued functions. Fred Almgren exploited the excess method for proving regularity theorems in the calculus of variations. His techniques yielded Holder continuous differentiability except for a small closed singular set. In the sixties and seventies Almgren refined and generalized his methods. Between 1974 and 1984 he wrote a 1,700-page proof that was his most ambitious development of his ground-breaking ideas. Originally, this monograph was available only as a three-volume work of limited circulation. The entire text is faithfully reproduced here. This book gives a complete proof of the interior regularity of an area-minimizing rectifiable current up to Hausdorff codimension 2. The argument uses the theory of Q-valued functions, which is developed in detail. For example, this work shows how first variation estimates from squash and squeeze deformations yield a monotonicity theorem for the normalized frequency of oscillation of a Q-valued function that minimizes a generalized Dirichlet integral. The principal features of the book include an extension theorem analogous to Kirszbraun's theorem and theorems on the approximation in mass of nearly flat mass-minimizing rectifiable currents by graphs and images of Lipschitz Q-valued functions The principal result of this paper is the interior regularity result of Theorem 5.22 which states, in particular, the following Theorem Suppose l, m, n, q are positive integers with l n, m 2, q 3. Frederick J. Almgren, Jr. ; Editors, Vladimir Scheffer & Jean E. Taylor. Includes Bibliographical References (p. 953-955).