arXiv · math/0312491
To solve problems of Gilbert Baumslag and Hanna Neumann, posed in the 1960's, we construct a nontrivial variety of groups all of whose noncyclic free groups are non-hopfian.
S. V. Ivanov, A. M. Storozhev. 2003-12-29. Non-hopfian relatively free groups. https://arxiv.org/abs/math/0312491
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