reserve a,b,c for set;
reserve r for Real,
  X for set,
  n for Element of NAT;

theorem Th35:
  for X being infinite set, A being Subset of X st A is finite
  holds A` is infinite
proof
  let X be infinite set, A be Subset of X;
  A \/ A` = [#]X by SUBSET_1:10
    .= X;
  hence thesis;
end;
