"Version: 20181001"--Title page verso.Includes bibliographical references.1. Introduction -- part I. String theory. 2. String theory -- 2.1. Actions, symmetries and solutions -- 2.2. Canonical quantization and Virasoro algebra -- 2.3. Spurious states and critical strings -- 2.4. Lightcone gauge quantization -- 2.5. Exercises3. Polyakov path integral -- 3.1. Gauge fixing and Fadeev-Popov ghosts …