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3 ideas
13288 | Consequence is truth-preserving, either despite substitutions, or in all interpretations [Koslicki] |
14506 | 'Roses are red; therefore, roses are colored' seems truth-preserving, but not valid in a system [Koslicki] |
8078 | Modus ponens is one of five inference rules identified by the Stoics [Chrysippus, by Devlin] |