amsmath

amsmath - AMS mathematical facilities for LATEX. The principal package in the AMS-LATEX distribution. It adapts for use in LATEX most of the mathematical features found in AMS-TEX; it is highly recommended as an adjunct to serious mathematical typesetting in LATEX. When amsmath is loaded, AMS-LATEX packages amsbsy (for bold symbols), amsopn (for operator names) and amstext (for text embedded in mathematics) are also loaded. amsmath is part of the LATEX required distribution; however, several contributed packages add still further to its appeal; examples are empheq, which provides functions for decorating and highlighting mathematics, and ntheorem, for specifying theorem (and similar) definitions.