let p be Element of CQC-WFF ; :: thesis: for x being bound_QC-variable holds (All x,('not' ('not' p))) <=> (All x,p) is valid
let x be bound_QC-variable; :: thesis: (All x,('not' ('not' p))) <=> (All x,p) is valid
( (All x,('not' ('not' p))) => (All x,p) is valid & (All x,p) => (All x,('not' ('not' p))) is valid ) by Th49;
hence (All x,('not' ('not' p))) <=> (All x,p) is valid by Lm14; :: thesis: verum