let p, q, r, s be Element of CQC-WFF ; :: thesis: ( p => q in TAUT & r => s in TAUT implies (p '&' r) => (q '&' s) in TAUT )
assume ( p => q in TAUT & r => s in TAUT ) ; :: thesis: (p '&' r) => (q '&' s) in TAUT
then ( (p '&' r) => (q '&' r) in TAUT & (q '&' r) => (q '&' s) in TAUT ) by Lm5, Th51;
hence (p '&' r) => (q '&' s) in TAUT by LUKASI_1:3; :: thesis: verum