let p be Element of CQC-WFF ; :: thesis: for y, x being bound_QC-variable st not y in still_not-bound_in p holds
(All x,p) => (All y,p) is valid
let y, x be bound_QC-variable; :: thesis: ( not y in still_not-bound_in p implies (All x,p) => (All y,p) is valid )
assume not y in still_not-bound_in p ; :: thesis: (All x,p) => (All y,p) is valid
then ( (All x,p) => p is valid & not y in still_not-bound_in (All x,p) ) by Th5, CQC_THE1:105;
hence (All x,p) => (All y,p) is valid by CQC_THE1:106; :: thesis: verum