@article{IM2_1991_37_1_a8,
     author = {D. Yu. Nogin},
     title = {Spirals of period~4 and  equations of {Markov} type},
     journal = {Izvestiya. Mathematics },
     pages = {209--226},
     publisher = {mathdoc},
     volume = {37},
     number = {1},
     year = {1991},
     language = {en},
     url = {http://geodesic.mathdoc.fr/item/IM2_1991_37_1_a8/}
}