@article{10_1017_S0017089500002287,
     author = {Evans, R. J.},
     title = {Free products of two real cyclic matrix groups},
     journal = {Glasgow mathematical journal},
     pages = {121--128},
     year = {1974},
     volume = {15},
     number = {2},
     doi = {10.1017/S0017089500002287},
     url = {http://geodesic.mathdoc.fr/articles/10.1017/S0017089500002287/}
}