On a theorem due to Cassels (Q1121331)

Let E be an elliptic curve over a finite extension of \({\mathbb{Q}}_ p\) in minimal Weierstrass form. Let x be a torsion point on E. A theorem of Cassels' describes the possible denominators of the co-ordinates of x depending on whether the order is a power of p or not. In this paper the author gives a different proof of Cassels' theorem depending on the properties of formal groups.