let p be Element of QC-WFF ; :: thesis: for V being non empty Subset of QC-variables holds Vars (('not' p),V) = Vars (p,V)
let V be non empty Subset of QC-variables; :: thesis: Vars (('not' p),V) = Vars (p,V)
set 9p = 'not' p;
A1: 'not' p is negative by QC_LANG1:def 17;
then the_argument_of ('not' p) = p by QC_LANG1:def 22;
hence Vars (('not' p),V) = Vars (p,V) by A1, Lm2; :: thesis: verum