Effectiveness of Walker's cancellation theorem

Abstract Walker's cancellation theorem for abelian groups tells us that if is finitely generated and and are such that , then . Deveau showed that the theorem can be effectivized, but not uniformly. In this paper, we expand on Deveau's initial analysis to show that the complexity of uniformly outputting an index of an isomorphism between and , given indices for , , , the isomorphism between and , and the rank of , is . Moreover, we find that the complexity remains even if the generators in the copies of are specified.