EntityQ3502995· pop 15· linked from 505 articlesundecidable problemSign in to savedecision problem for which it is impossible to construct an algorithm that always leads to a correct yes-or-no answerConnectionssemantic theory of truthEntitynatural numberEntitymathematical logicEntityGödel's incompleteness theoremsEntitystringEntitycountable setEntityfirst-order logicEntityformal systemEntityZermelo–Fraenkel set theoryEntityconsistencyEntityaxiomatic systemEntityrecursive setEntitysemantics of logicEntityrecursively enumerable setEntitystructureEntityground expressionEntitydiagramEntitylogicEntityAlan TuringEntityInternational Standard Book NumberEntityCategoriesComputability theoryLogic in computer scienceUndecidable problems