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Ideas for 'Classical Cosmology (frags)', 'Logic for Philosophy' and 'Physics and Philosophy'

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6. Mathematics / B. Foundations for Mathematics / 4. Axioms for Number / e. Peano arithmetic 2nd-order

13701

A single second-order sentence validates all of arithmetic - but this can't be proved axiomatically [Sider]

6. Mathematics / C. Sources of Mathematics / 4. Mathematical Empiricism / b. Indispensability of mathematics

17536

If it can't be expressed mathematically, it can't occur in nature? [Heisenberg]