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

theorem Th2:
  (p => (q => r)) => ((p => q) => (p => r)) in CnIPC (X)
proof
  T is IPC_theory & X c= T implies (p => (q => r)) => ((p => q) => (p => r
  )) in T;
  hence thesis by Def15;
end;
