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

theorem Th14:
  p => p in HP_TAUT
proof
A1: p => (p => p) in HP_TAUT by Def10;
A2: p => ((p => p) => p) in HP_TAUT by Def10;
  (p => ((p => p) => p)) => ((p => (p => p)) => (p => p)) in HP_TAUT by Def10;
  then (p => (p => p)) => (p => p) in HP_TAUT by A2,Def10;
  hence thesis by A1,Def10;
end;
