reserve A for QC-alphabet;
reserve p, q, r, s for Element of CQC-WFF(A);

theorem
  p => q in TAUT(A) & r => s in TAUT(A) implies ( p '&' r ) => ( q '&' s )
in TAUT(A)
proof
  assume p => q in TAUT(A) & r => s in TAUT(A);
  then
  ( p '&' r ) => ( q '&' r ) in TAUT(A) & ( q '&' r ) => ( q '&' s ) in TAUT(A)
  by Lm5,Th51;
  hence thesis by LUKASI_1:3;
end;
