reserve M for non empty set;
reserve V for ComplexNormSpace;
reserve f,f1,f2,f3 for PartFunc of M,V;
reserve z,z1,z2 for Complex;

theorem Th24:
  -(-f) = f
proof
  thus -(-f) = (-1r)(#)(-f) by Th23
    .= (-1r)(#)((-1r)(#)f) by Th23
    .= ((-1r)*(-1r))(#)f by Th14
    .= f by Th18,COMPLEX1:def 4;
end;
