let p be Element of CQC-WFF ; :: thesis: for x being bound_QC-variable holds ('not' (Ex x,('not' p))) <=> (All x,p) is valid
let x be bound_QC-variable; :: thesis: ('not' (Ex x,('not' p))) <=> (All x,p) is valid
( ('not' (Ex x,('not' p))) => (All x,p) is valid & (All x,p) => ('not' (Ex x,('not' p))) is valid ) by Th53;
hence ('not' (Ex x,('not' p))) <=> (All x,p) is valid by Lm14; :: thesis: verum