reserve E,F,G for RealNormSpace;
reserve f for Function of E,F;
reserve g for Function of F,G;
reserve a,b,c for Point of E;
reserve t for Real;

theorem Th23:
  (a-reflection)/" = a-reflection
  proof
    set R = a-reflection;
A1: rng R = [#]E by FUNCT_2:def 3;
A2: R/" = (R qua Function)" by TOPS_2:def 4;
    R*R = id E by Th17;
    hence thesis by A1,A2,FUNCT_2:30;
  end;
