Makanin's algorithm is not primitive recursive

Antoni Kościelski, Leszek Pacholski
1998 Theoretical Computer Science  
We prove that, contrary to the common belief, the algorithm deciding sat&ability of equations in free groups, given by Makanin, is not primitive recursive.
doi:10.1016/s0304-3975(96)00321-0 fatcat:4e6ddxuxrvhntnx43z4zeskc4u