The groups which may be generated by two operators $s_1 ,s_2 $ satisfying the equation $\left( {s_1 s_2 } \right)^\alpha = \left( {s_2 s_1 } \right)^\beta $, $\alpha$ and $\beta$ being relatively prime

G. A. Miller
1909 Bulletin of the American Mathematical Society  
doi:10.1090/s0002-9904-1909-01857-9 fatcat:yvtyre6jibdlfkxfhvk773ipyi