Frege and Gödel: two fundamental texts in mathematical logic

Begriffsschrift, a formula language, modeled upon that of arithmetic, for pure thought (1879), by G. Frege.

Some metamathematical results on completeness and consistency; On formally undecidable propositions of Principia mathematica and related systems I; and On completeness and consistency (1930b, 1931, and 1931a), by K. Gödel.

Bibliography (p. [111]-116)