isogeny การใช้

This is an equivalence relation, symmetry being due to the existence of the dual isogeny.
Points on correspond to pairs of elliptic curves admitting an isogeny of degree with cyclic kernel.
The two curves are called " isogenous " if there is an isogeny between them.
To call this a direct sum decomposition, we should work in the category of abelian varieties up to isogeny.
As above, every isogeny induces homomorphisms of the groups of the k-valued points of the abelian varieties.