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

theorem Th62:
  ( p => q ) => (( s 'or' p ) => ( s 'or' q )) in IPC-Taut
proof
  set P = s 'or' p, Q = s 'or' q;
A1: s => Q in IPC-Taut by Def14;
A2: (p => q) => (p => Q) in IPC-Taut by Th59;
  (s => Q) => ((p => Q) => (P => Q)) in IPC-Taut by Def14;
  then (p => Q) => (P => Q) in IPC-Taut by A1,Def14;
  hence thesis by A2,Th26;
end;
