@article{CM_1968__20__88_0, author = {Henkin, Leon}, title = {Relativization with respect to formulas and its use in proofs of independence}, journal = {Compositio Mathematica}, publisher = {Wolters-Noordhoff Publishing}, volume = {20}, year = {1968}, pages = {88-106}, zbl = {0155.02301}, mrnumber = {234812}, language = {en}, url = {http://www.numdam.org/item/CM_1968__20__88_0} }

Henkin, Leon. Relativization with respect to formulas and its use in proofs of independence. Compositio Mathematica, Volume 20 (1968) , pp. 88-106. http://www.numdam.org/item/CM_1968__20__88_0/

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