Hilbert's Nullstellensatz Algebraic Geometry Collinearity and the Group Law Algebraic Geometry Riemann–Hurwitz Formula Algebraic Geometry Curves of Degree at Most 2 Meet in at Most 4 Points Algebraic Geometry Differentials Are Well-Defined and Chain Rule Holds Algebraic Geometry Projective Closure of an Affine Variety via Homogenisation of the Ideal Algebraic Geometry Normal Form for Quadrics Algebraic Geometry Unique Effective Representative When $\ell(D) = 1$ Algebraic Geometry