theorem Th21: :: FRECHET2:21

for T being non empty TopSpace st T is Frechet holds
for A, B being Subset of T holds
( Cl_Seq ({} T) = {} & A c= Cl_Seq A & Cl_Seq (A \/ B) = (Cl_Seq A) \/ (Cl_Seq B) & Cl_Seq (Cl_Seq A) = Cl_Seq A )