let p, q, r be Element of CQC-WFF ; :: thesis: ( p => (q => r) is valid implies (p '&' q) => r is valid )
A1: (p => (q => r)) => ((p '&' q) => r) in TAUT by PROCAL_1:32;
assume p => (q => r) in TAUT ; :: according to CQC_THE1:def 10 :: thesis: (p '&' q) => r is valid
hence (p '&' q) => r in TAUT by A1, CQC_THE1:46; :: according to CQC_THE1:def 10 :: thesis: verum