theorem Th47: :: CQC_THE2:47

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