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
  A c= B+ & n > 0 implies A |^.. n c= B+
proof
  assume that
A1: A c= B+ and
A2: n > 0;
  A c= B |^.. 1 by A1,Th50;
  then A |^.. n c= B |^.. 1 by A2,Th29;
  hence thesis by Th50;
end;
