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

theorem Th46:
  ( p '&' q ) => ( q '&' p ) in IPC-Taut
proof
  set P = p '&' q;
A1: P => q in IPC-Taut by Def14;
A2: P => p in IPC-Taut by Def14;
  ( P => q ) => (( P => p ) => ( P => ( q '&' p ))) in IPC-Taut by Th38;
  then ( P => p ) => ( P => ( q '&' p )) in IPC-Taut by A1,Def14;
  hence thesis by A2,Def14;
end;
