let A be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF A st p => (q => r) is valid holds
q => (p => r) is valid
let p, q, r be Element of CQC-WFF A; :: thesis: ( p => (q => r) is valid implies q => (p => r) is valid )
assume p => (q => r) is valid ; :: thesis: q => (p => r) is valid
then p => (q => r) in TAUT A by CQC_THE1:def 10;
hence q => (p => r) in TAUT A by Th15; :: according to CQC_THE1:def 10 :: thesis: verum