Defect (geometry): Geometry, Hyperbolic Triangle, Spherical Gauss Bonnet Theorem

Gauss Bonnet Theorem: Differential Geometry, Surface, Carl Friedrich

Apollonius' Theorem: Geometry, Theorem, Median (geometry), Triangle

CPCTC: Geometry, Theorem, Congruence (geometry), Triangle

Ultraparallel Theorem: Hyperbolic Geometry, Ultraparallel, Perpendicular