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Published online by Cambridge University Press: 20 November 2018
Let $J$ be an abelian variety and $A$ be an abelian subvariety of $J$ , both defined over $Q$. Let $x$ be an element of ${{H}^{1}}\left( Q,\,A \right)$. Then there are at least two definitions of $x$ being visible in $J$: one asks that the torsor corresponding to $x$ be isomorphic over $Q$ to a subvariety of $J$, and the other asks that $x$ be in the kernel of the natural map $ {{H}^{1}}\left( Q,\,A \right)\,\to \,{{H}^{1}}\left( \text{Q},\,J \right)$. In this article, we clarify the relation between the two definitions.