let A be QC-alphabet ; :: thesis: for p, q being QC-formula of A holds still_not-bound_in (p 'or' q) = (still_not-bound_in p) \/ (still_not-bound_in q)
let p, q be QC-formula of A; :: thesis: still_not-bound_in (p 'or' q) = (still_not-bound_in p) \/ (still_not-bound_in q)
A1: the_right_disjunct_of (p 'or' q) = q by QC_LANG2:29;
( p 'or' q is disjunctive & the_left_disjunct_of (p 'or' q) = p ) by QC_LANG2:29, QC_LANG2:def 10;
hence still_not-bound_in (p 'or' q) = (still_not-bound_in p) \/ (still_not-bound_in q) by A1, Th13; :: thesis: verum