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5. Theory of Logic / H. Proof Systems / 1. Proof Systems

[general ideas about the different proof systems]

4 ideas
Proof theory began with Frege's definition of derivability [Frege, by Prawitz]
Logical proof just explicates complicated tautologies [Wittgenstein]
An 'informal proof' is in no particular system, and uses obvious steps and some ordinary English [Bostock]
'Induction' and 'recursion' on complexity prove by connecting a formula to its atomic components [Burgess]