<P> In the mathematical field of topology, a G set is a subset of a topological space that is a countable intersection of open sets . The notation originated in Germany with G for Gebiet (German: area, or neighbourhood) meaning open set in this case and δ for Durchschnitt (German: intersection). The term inner limiting set is also used . G sets, and their dual F sets, are the second level of the Borel hierarchy . </P> <P> In a topological space a G set is a countable intersection of open sets . The G sets are exactly the level Π 2 0 (\ displaystyle \ mathbf (\ Pi) _ (2) ^ (0)) sets of the Borel hierarchy . </P>

Set of points of continuity is g delta