Introduction to Differential Geometry by Mark Powell
ID: introduction-to-differential-geometry-by-mark-powell
Consulted passages: Part I §§2.1, 2.5–2.8 (arc length, curvature, torsion, spherical frames); Part VI §§7.1–7.5 (boundary terms, geodesic polygons, global Gauss-Bonnet and proof).
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