Theorem : Let $A$ be an abelian varieties of dimension $d$ over a field $k$, non-archimedian valued complete, i.e. $\mathbb{Q}_p$, then $A(k)$ contains a subgroup of finite index analytically isomorphic and homeomorphic to $I \oplus I \oplus \ldots \oplus I$ ($d$ summands) where $I$ is the ring of integers of $k$.
This is a theorem written in a paper by Arthur Mattock in 1955. I was wondering if someone knows where one can find any other proof of his theorem.
P.S. the name of the paper is Abelian varieties over $p$-adic ground fields.