let A be QC-alphabet ; :: thesis: for x being bound_QC-variable of A
for p being Element of QC-WFF A holds Fixed (Ex (x,p)) = Fixed p
let x be bound_QC-variable of A; :: thesis: for p being Element of QC-WFF A holds Fixed (Ex (x,p)) = Fixed p
let p be Element of QC-WFF A; :: thesis: Fixed (Ex (x,p)) = Fixed p
Ex (x,p) = 'not' (All (x,('not' p))) by QC_LANG2:def 5;
hence Fixed (Ex (x,p)) = Fixed (All (x,('not' p))) by Th39
.= Fixed ('not' p) by Th44
.= Fixed p by Th39 ;
:: thesis: verum