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

theorem Th63:
  p => q in IPC-Taut implies ( s 'or' p ) => ( s 'or' q ) in IPC-Taut
proof
  assume
A1: p => q in IPC-Taut;
  ( p => q ) => (( s 'or' p ) => ( s 'or' q )) in IPC-Taut by Th62;
  hence thesis by A1,Def14;
end;
