
theorem Th3:
for X,A be set holds chi(A,X) is without+infty without-infty
proof
   let X,A be set;
   rng chi(A,X) c= {0,1} by FUNCT_3:39; then
   not +infty in rng chi(A,X) & not -infty in rng chi(A,X);
   hence chi(A,X) is without+infty without-infty by MESFUNC5:def 3,def 4;
end;
