EntityQ127244· pop 8· linked from 45 articlesGδ setSign in to savecountable intersection of open setsConnectionsmetric spaceEntitynormal spaceEntityGermanEntityFrenchEntityInternational Standard Book NumberEntitytopologyEntityrational numberEntitydigital object identifierEntityderivativeEntityirrational numberEntityempty setEntitysubsetEntitycontinuous functionEntityJSTOREntityintersectionEntitytopological spaceEntityhomeomorphismEntitycomplementEntityzero of a functionEntityreal analysisEntityCategoriesDescriptive set theoryGeneral topology