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