reserve E, x, y, X for set;
reserve A, B, C for Subset of E^omega;
reserve a, a1, a2, b for Element of E^omega;
reserve i, k, l, m, n for Nat;

theorem
  x in A & x <> <%>E implies A+ <> {<%>E}
proof
  assume that
A1: x in A and
A2: x <> <%>E;
  A+ = A |^.. 1 by Th50;
  hence thesis by A1,A2,Th14;
end;
