let A be QC-alphabet ; :: thesis: for s, q, p being Element of CQC-WFF A st s => (q => p) in TAUT A & q in TAUT A holds
s => p in TAUT A
let s, q, p be Element of CQC-WFF A; :: thesis: ( s => (q => p) in TAUT A & q in TAUT A implies s => p in TAUT A )
assume s => (q => p) in TAUT A ; :: thesis: ( not q in TAUT A or s => p in TAUT A )
then q => (s => p) in TAUT A by Th15;
hence ( not q in TAUT A or s => p in TAUT A ) by CQC_THE1:46; :: thesis: verum