# Introduction

## Chapter 1. Introduction

Regina is a software package for low-dimensional topologists. Historically, its main strengths lie in 3-manifold topology: it has a highly optimised toolkit with a focus on normal surface theory, angle structures, and the combinatorial structures of triangulations, and it now performs many high-level topological algorithms for 3-manifolds. Since version 5.0, Regina also offers a rich toolkit for triangulated 4-manifolds, plus basic combinatorial support for manifolds of dimension 5–15. For more on these and its many other features, see the full feature set later in this introduction.

## Getting Started

Not sure how to start Regina? You can find it in your main applications or programs menu; follow this link for details and screenshots.

The best way to become familiar with Regina is simply to play around with it. Regina ships with several example files, including a number of censuses of 3-manifold triangulations. Most of these examples can be accessed through the File→Open Example menu when running Regina.

For an excellent starting point, try File→Open Example→Introductory Examples, which illustrates most of the structures that Regina can work with. The users' handbook (which you are reading now) also includes a number of sample Python sessions that illustrate how Regina's in-built Python scripting can be used.

The graphical user interface offers extensive assistance through tooltips and "What's This?" texts. If you ever want to know what element of the user interface means (such a button or a text field), just press Shift+F1 and click on the thing you would like to know more about.