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

theorem
  A c= B? implies A? c= B?
proof
  <%>E in B? by Th78;
  then
A1: {<%>E} c= B? by ZFMISC_1:31;
  assume A c= B?;
  then {<%>E} \/ A c= B? by A1,XBOOLE_1:8;
  hence thesis by Th76;
end;
