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Ideas for 'The Character of Physical Law', 'What is Logic?st2=Ian Hacking' and 'On Eternal and Immutable Morality'

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3 ideas

4. Formal Logic / B. Propositional Logic PL / 2. Tools of Propositional Logic / d. Basic theorems of PL

13834

Gentzen's Cut Rule (or transitivity of deduction) is 'If A |- B and B |- C, then A |- C' [Hacking]

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Only Cut reduces complexity, so logic is constructive without it, and it can be dispensed with [Hacking]

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'Thinning' ('dilution') is the key difference between deduction (which allows it) and induction [Hacking]