EntityQ926996· pop 12· linked from 74 articlesfirst-countable spaceSign in to savetopological space in which every point admits a countable neighborhood basisConnectionssecond-countable spaceEntityorder topologyEntitymathematicsEntityInternational Standard Book NumberEntitytopologyEntitysequenceEntitysubsetEntitycontinuous functionEntitymetric spaceEntitytopological spaceEntitynumber lineEntityballEntitylimit of a sequenceEntitylimit of a functionEntitycountable setEntityopen setEntityneighborhoodEntityalgebraic varietyEntitylimit pointEntityuncountable setEntityCategoriesGeneral topologyProperties of topological spaces