no. 3
On the form of functions which preserve regressive isols
Compositio Mathematica, Tome 26 (1973) no. 3, pp. 283-302. 
@article{CM_1973__26_3_283_0,
     author = {Ellentuck, Erik},
     title = {On the form of functions which preserve regressive isols},
     journal = {Compositio Mathematica},
     pages = {283--302},
     publisher = {Noordhoff International Publishing},
     volume = {26},
     number = {3},
     year = {1973},
     zbl = {0272.02067},
     mrnumber = {344102},
     language = {en},
     url = {www.numdam.org/item/CM_1973__26_3_283_0/}
}
Ellentuck, Erik. On the form of functions which preserve regressive isols. Compositio Mathematica, Tome 26 (1973) no. 3, pp. 283-302. http://www.numdam.org/item/CM_1973__26_3_283_0/

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