let a be real number ; :: thesis: Cl ].-infty,a.[ = ].-infty,a.]
reconsider A = ].-infty,a.[ as Subset of R^1 by TOPMETR:24;
Cl A = ].-infty,a.] by Th77;
hence Cl ].-infty,a.[ = ].-infty,a.] by TOPREAL6:80; :: thesis: verum