Editing Nagell–Lutz theorem (section)

==Generalizations==
The Nagell–Lutz theorem generalizes to arbitrary number fields and more
general cubic equations.<ref name="general">See, for example, 
[https://books.google.com/books?id=6y_SmPc9fh4C&dq=Silverman+torsion+points&pg=PA220 Theorem VIII.7.1] of
[[Joseph H. Silverman]] (1986), "The arithmetic of elliptic curves",
Springer, {{isbn|0-387-96203-4}}.</ref>  
For curves over the rationals, the generalization says that, for a nonsingular cubic curve whose Weierstrass form
:<math>y^2 +a_1 x y + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6 </math>
has integer coefficients, any rational point <math>P = (x,y)</math> of finite
order must have integer coordinates, or else have order 2 and
coordinates of the form <math>x=m/4</math>, <math>y=n/8</math>, for ''m'' and ''n'' integers.