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

theorem Th43:
  ( (p '&' s) => q ) => ((p '&' s) => (q '&' s)) in IPC-Taut
proof
  set P = p '&' s;
A1: ( P => q ) => (( P => s ) => ( P => ( q '&' s ))) in IPC-Taut by Th38;
  P => s in IPC-Taut by Def14;
  hence thesis by A1,Th32;
end;
