theorem Th71: :: CQC_THE2:71

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