theorem Th63: :: TOPGEN_4:63

for T being non empty TopSpace
for X being Subset-Family of T ex Y being compl-closed all-open-containing closed_for_countable_unions Subset-Family of T st
( X c= Y & ( for Z being compl-closed all-open-containing closed_for_countable_unions Subset-Family of T st X c= Z holds
Y c= Z ) )