EntityQ649732· pop 35· linked from 612 articlesformal systemSign in to saveany well-defined system of abstract thought based on the model of mathematicsConnectionsaxiomEntitymathematical logicEntityrecursive setEntitystructureEntitysemantic theory of truthEntityformal languageEntitystringEntityfirst-order logicEntityPeano axiomsEntityfoundations of mathematicsEntityformal grammarEntityformal methodsEntityrule of inferenceEntityinterpretationEntitysemantics of logicEntityrecursively enumerable setEntitysubstitutionEntityground expressionEntitydiagramEntityEuropeEntityCategories1st-millennium BC introductions4th century BC in IndiaCleanup tagged articles with a reason field from October 2023Formal languagesFormal logicFormal systemsMetalogicSyntax (logic)