| 1917 | works |
| p.125 | 15927 | Definition just needs negation, known variables, conjunction, disjunction, substitution and quantification [Lavine] |
| 1949 | Phil of Mathematics and Natural Science |
| 25-7 | p.160 | 10246 | The limit of science is isomorphism of theories, with essences a matter of indifference |