An introduction to groups groupoids and their representations Cover; Title Page; Copyright Page; Dedication; Preface; Acknowledgements; Table of Contents; Introduction; PART I: WORKING WITH CATEGORIES AND GROUPOIDS; 1: Categories: Basic Notions and Examples; 1.1 Introducing the main characters; 1.1.1 Connecting dots graphs and quivers; 1.1.2 Drawing simple quivers and categories; 1.1.3 Relations inverses and some interesting problems; 1.2 Categories: Formal definitions; 1.2.1 Finite categories; 1.2.2 Abstract categories; 1.3 A categorical definition of groupoids and groups; 1.4 Historical notes and additional comments