theorem Th44:
  still_not-bound_in (p) c= Bound_Vars(p) implies
  still_not-bound_in ('not' p) c= Bound_Vars('not' p)
proof
  'not' p is negative by QC_LANG1:def 19;
  then Bound_Vars('not' p) = Bound_Vars(the_argument_of ('not' p)) by
SUBSTUT1:4;
  then
A1: Bound_Vars('not' p) = Bound_Vars(p) by QC_LANG2:1;
  assume still_not-bound_in (p) c= Bound_Vars(p);
  hence thesis by A1,QC_LANG3:7;
end;
