:: deftheorem GTDef defines GenTop ROUGHS_4:def 25 :
for X being set
for f being Function of (bool X),(bool X)
for b₃ being Subset-Family of X holds
( b₃ = GenTop f iff for x being object holds
( x in b₃ iff ex S being Subset of X st
( S = x & S is f -closed ) ) );