EntityQ798572· pop 16· linked from 25 articlesPost correspondence problemSign in to saveundecidable decision problemConnectionsInternational Standard Book NumberEntitydigital object identifierEntitysequenceEntityTuring machineEntityregular expressionEntityQ118398EntitymonoidEntityfinite-state machineEntityChomsky hierarchyEntityQ22908627Entityhalting problemEntitygroup homomorphismEntityNP-completeEntitynilpotent elementEntitydecision problemEntityHandle SystemEntityEmil Leon PostEntityboolean satisfiability problemEntityregular languageEntityconjugacy classEntityCategoriesComputability theoryTheory of computationUndecidable problems