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

theorem Th29:
  s => (q => p) in HP_TAUT & q in HP_TAUT implies s => p in HP_TAUT
proof
  assume that
A1: s => (q => p) in HP_TAUT and
A2: q in HP_TAUT;
  (s => (q => p)) => (q => (s => p)) in HP_TAUT by Th26;
  then q => (s => p) in HP_TAUT by A1,Def10;
  hence thesis by A2,Def10;
end;
