Find in terms of three non-zero vectors \(\mathbf{a}\), \(\mathbf{b}\), \(\mathbf{c}\), (such that \(\mathbf{a}\) is not perpendicular to \(\mathbf{b}\)) the most general vector \(\mathbf{r}\) which satisfies $$\mathbf{a} \times (\mathbf{b} \times (\mathbf{c} \times \mathbf{r})) = \mathbf{0},$$ examining carefully any configurations which give rise to exceptional cases.