let Al be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF Al holds (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) is valid
let p, q, r be Element of CQC-WFF Al; :: thesis: (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) is valid
(p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) in TAUT Al

proof

TAUT Al is being_a_theory by Th11;
hence (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) in TAUT Al ; :: thesis: verum

end;

hence (p => q) => (('not' (q '&' r)) => ('not' (p '&' r))) is valid ; :: thesis: verum