Appendix : “Picard groups of Zariski surfaces”
Compositio Mathematica, Tome 54 (1985) no. 1, pp. 37-40. 
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     author = {Blass, Piotr and Lang, Jeffrey},
     title = {Appendix : {{\textquotedblleft}Picard} groups of {Zariski} surfaces{\textquotedblright}},
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     publisher = {Martinus Nijhoff Publishers},
     volume = {54},
     number = {1},
     year = {1985},
     mrnumber = {1557073},
     zbl = {0624.14022},
     language = {en},
     url = {http://www.numdam.org/item/CM_1985__54_1_37_0/}
}
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Blass, Piotr; Lang, Jeffrey. Appendix : “Picard groups of Zariski surfaces”. Compositio Mathematica, Tome 54 (1985) no. 1, pp. 37-40. http://www.numdam.org/item/CM_1985__54_1_37_0/

[1] P. Blass: Picard groups of Zariski surfaces I. Comp. Math. 54 (1985) 3-36. | Numdam | MR | Zbl

[2] P. Blass: Groupes de Picard des surfaces de Zariski. Comptes Rendus des Seances de I'Academie des Sciences, I-315, 19 septembre 1983. | MR

[3] Jeffrey Lang: The divisor class group of the surface zpn = G(x,y) over fields of characteristic p > 0. Journal of Algebra (2) 1983. | Zbl