Let $\phi$ be a Drinfeld module over a function field $K$. It is known that if the rank of $\phi$ is 1, then it is isomorphic over $K$ to one defined over $O_K$. Is it true that if the rank of $\phi$ is arbitrary, then it is isogenous over $K$ to one defined over $O_K$?
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included the field of definition of the isomorphism/isogeny; corrected some grammar
Isogeny of Drinfeld module
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