theorem Th28:
  seq(n,0.L) = 0_.L
  proof
    let m be Element of NAT;
    per cases;
    suppose m = n;
      hence seq(n,0.L).m = 0.L by Th24
      .= (0_.L).m;
    end;
    suppose m <> n;
      hence seq(n,0.L).m = (0_.L).m by FUNCT_7:32;
    end;
  end;
