reserve n for Element of NAT,
  a, r for Real,
  x for Point of TOP-REAL n;

theorem Th3:
  the carrier of Tdisk(x,r) = cl_Ball(x,r)
proof
  [#]Tdisk(x,r) = cl_Ball(x,r) by PRE_TOPC:def 5;
  hence thesis;
end;
