let p, q, r be Element of CQC-WFF ; :: thesis: ( p => q is valid implies (r '&' p) => (r '&' q) is valid )
assume p => q in TAUT ; :: according to CQC_THE1:def 11 :: thesis: (r '&' p) => (r '&' q) is valid
hence (r '&' p) => (r '&' q) in TAUT by PROCAL_1:50; :: according to CQC_THE1:def 11 :: thesis: verum