Melvin Fitting. Elementary Formal Systems for Hyperarithmetical Relations. Math. Log. Q., 24(1-6):25-30, 1978. [doi]
@article{Fitting78,
title = {Elementary Formal Systems for Hyperarithmetical Relations},
author = {Melvin Fitting},
year = {1978},
doi = {10.1002/malq.19780240104},
url = {http://dx.doi.org/10.1002/malq.19780240104},
researchr = {https://researchr.org/publication/Fitting78},
cites = {0},
citedby = {0},
journal = {Math. Log. Q.},
volume = {24},
number = {1-6},
pages = {25-30},
}