// AP Computer Science, AB Exam, 1996, Question 3, part A in C++

bool ValsLess(TreeNode * t, int k)
//postcondition: returns true if t is NULL or if
//               all values stored in tree represented
//               by t are less than k; otherwise
//               returns false
{
    if (t == NULL) return true;           // empty tree?

    return t->info < k &&
	   ValsLess(t->left,k)  &&
	   ValsLess(t->right,k);
}