theorem Th28: :: VALUAT_1:28

for Al being QC-alphabet
for A being non empty set
for x being bound_QC-variable of Al
for v being Element of Valuations_in (Al,A)
for p being Element of CQC-WFF Al
for J being interpretation of Al,A st J,v |= p & not x in still_not-bound_in p holds
for w being Element of Valuations_in (Al,A) st ( for y being bound_QC-variable of Al st x <> y holds
w . y = v . y ) holds
J,w |= p by Th27;