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

theorem :: Modus ponendo ponens
  q => ((q => p) => p) in HP_TAUT
proof
A1: ((q => p) => (q => p)) => (q => ((q => p) => p)) in HP_TAUT by Th26;
  (q => p) => (q => p) in HP_TAUT by Th14;
  hence thesis by A1,Def10;
end;
