@article{42801,
  abstract     = {{We exhibit a practical algorithm for solving the constructive membership problem for discrete free subgroups of rank 2 in PSL₂(R) or SL₂(R). This algorithm, together with methods for checking whether a two-generator subgroup of PSL₂(R) or SL₂(R) is discrete and free, have been implemented in Magma for groups defined over real algebraic number fields.}},
  author       = {{Kirschmer, Markus and LEEDHAM-GREEN, CHARLES}},
  issn         = {{0017-0895}},
  journal      = {{Glasgow Mathematical Journal}},
  keywords     = {{General Mathematics}},
  number       = {{1}},
  pages        = {{173--180}},
  publisher    = {{Cambridge University Press (CUP)}},
  title        = {{{Computing with subgroups of the modular group }}},
  doi          = {{10.1017/s0017089514000202}},
  volume       = {{57}},
  year         = {{2014}},
}