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 'or' r ) => ( q 'or' s )
in TAUT(A)
proof
  assume p => q in TAUT(A) & r => s in TAUT(A);
  then ( p 'or' r ) => ( q 'or' r ) in TAUT(A) & ( q 'or' r ) => ( q 'or' s )
 in
  TAUT(A) by Lm6,Lm7;
  hence thesis by LUKASI_1:3;
end;
