let A be QC-alphabet ; :: thesis: for p, q, r being Element of CQC-WFF A
for X being Subset of (CQC-WFF A) st X |- p => (q => r) & X |- q holds
X |- p => r
let p, q, r be Element of CQC-WFF A; :: thesis: for X being Subset of (CQC-WFF A) st X |- p => (q => r) & X |- q holds
X |- p => r
let X be Subset of (CQC-WFF A); :: thesis: ( X |- p => (q => r) & X |- q implies X |- p => r )
assume X |- p => (q => r) ; :: thesis: ( not X |- q or X |- p => r )
then X |- q => (p => r) by Th63;
hence ( not X |- q or X |- p => r ) by CQC_THE1:55; :: thesis: verum