theorem
  p=h.x & q=h.y & not y in still_not-bound_in h implies All(x,All(y,q))
  => All(x,p) is valid
proof
  assume p=h.x & q=h.y & not y in still_not-bound_in h;
  then All(x,All(y,q) => p) is valid by Th23,Th25;
  hence thesis by Th31;
end;
