An example of FOL using metatheory: Formalizing reasoning systems and introducing derived inference rules

Weyhrauch, R. W. (1982). An example of FOL using metatheory: Formalizing reasoning systems and introducing derived inference rules. In Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics) (Vol. 138 LNCS, pp. 151–158). Springer Verlag. https://doi.org/10.1007/BFb0000057