  This book is an invitation to discover advanced topics in category theory
through concrete, real-world examples. It aims to give a tour: a gentle, quick
introduction to guide later exploration. The tour takes place over seven
sketches, each pairing an evocative application, such as databases, electric
circuits, or dynamical systems, with the exploration of a categorical
structure, such as adjoint functors, enriched categories, or toposes.
  No prior knowledge of category theory is assumed.
  A feedback form for typos, comments, questions, and suggestions is available
here:
https://docs.google.com/document/d/160G9OFcP5DWT8Stn7TxdVx83DJnnf7d5GML0_FOD5Wg/edit
