let A be QC-alphabet ; :: thesis: for p, q, s being Element of CQC-WFF A st s => (q => p) in TAUT A & q in TAUT A & s in TAUT A holds
p in TAUT A
let p, q, s be Element of CQC-WFF A; :: thesis: ( s => (q => p) in TAUT A & q in TAUT A & s in TAUT A implies p in TAUT A )
assume ( s => (q => p) in TAUT A & q in TAUT A ) ; :: thesis: ( not s in TAUT A or p in TAUT A )
then s => p in TAUT A by Th16;
hence ( not s in TAUT A or p in TAUT A ) by CQC_THE1:46; :: thesis: verum