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@article{FEVAU59, author = {Feferman, Solomon and Vaught, Robert}, doi = {10.4064/fm-47-1-57-103}, journal = {Fundamenta Mathematicae}, pages = {57--103}, sha256 = {2C504C89902FB91CEECDD3A12243B31AA15481B9195C894A693CD1B0A259D1A7}, title = {The first order properties of products of algebraic systems}, volume = {47}, year = {1959} }