theorem Th49: :: CQC_THE2:49

for A being QC-alphabet
for p being Element of CQC-WFF A
for x being bound_QC-variable of A holds
( ('not' (Ex (x,('not' p)))) => (All (x,p)) is valid & (All (x,p)) => ('not' (Ex (x,('not' p)))) is valid )