reserve T, X, Y for Subset of HP-WFF;
reserve p, q, r, s for Element of HP-WFF;

theorem Th2:
  p => (q => (p '&' q)) in CnPos (X)
proof
  T is Hilbert_theory & X c= T implies p => (q => (p '&' q)) in T;
  hence thesis by Def11;
end;
