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

theorem Th59:
  (p => q) => (p => (s 'or' q)) in IPC-Taut
proof
A1: (q => (s 'or' q)) => ((p => q) => (p => (s 'or' q))) in IPC-Taut by Th22;
  q => (s 'or' q) in IPC-Taut by Def14;
  hence thesis by A1,Def14;
end;
