reserve T, X, Y for Subset of MC-wff;
reserve p, q, r, s for Element of MC-wff;

theorem :: Modus ponendo ponens
  q => ((q => p) => p) in IPC-Taut
proof
A1: ((q => p) => (q => p)) => (q => ((q => p) => p)) in IPC-Taut by Th29;
  (q => p) => (q => p) in IPC-Taut by Th17;
  hence thesis by A1,Def14;
end;
