Warren D. Goldfarb. On the effective ω-rule. Math. Log. Q., 21(1):409-412, 1975. [doi]
@article{Goldfarb75, title = {On the effective ω-rule}, author = {Warren D. Goldfarb}, year = {1975}, doi = {10.1002/malq.19750210155}, url = {http://dx.doi.org/10.1002/malq.19750210155}, researchr = {https://researchr.org/publication/Goldfarb75}, cites = {0}, citedby = {0}, journal = {Math. Log. Q.}, volume = {21}, number = {1}, pages = {409-412}, }