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 & (All x,p) => (All x,('not' ('not' p))) is valid )
let x be bound_QC-variable; :: thesis: ( (All x,('not' ('not' p))) => (All x,p) is valid & (All x,p) => (All x,('not' ('not' p))) is valid )
( All x,(('not' ('not' p)) => p) is valid & All x,(p => ('not' ('not' p))) is valid ) by Th26;
hence ( (All x,('not' ('not' p))) => (All x,p) is valid & (All x,p) => (All x,('not' ('not' p))) is valid ) by Th35; :: thesis: verum