Makanin's Algorithm is not Primitive Recursive

@article{Koscielski1998MakaninsAI,
  title={Makanin's Algorithm is not Primitive Recursive},
  author={Antoni Koscielski and Leszek Pacholski},
  journal={Theor. Comput. Sci.},
  year={1998},
  volume={191},
  pages={145-156}
}
Abstract We prove that, contrary to the common belief, the algorithm deciding satisfiability of equations in free groups, given by Makanin, is not primitive recursive.