On the solution of algebraic equations in infinite series
Preston A Lambert · Bulletin of the American Mathematical Society · 1908
SOLUTION OF ALGEBRAIC EQUATIONS.467 normal to a point (x, y, z) on the surface is given by an expression of the formin which A and B are constants and the omitted terms are of the third order at least, and that when the given point is not a principal center of curvature the coefficients A and B do not vanish.If, however, the given point be a principal center of curvature, A or B will vanish and an examination of the sign of the non-vanishing coefficient will easily yield the first three theorems.