If $\overline{a}, \overline{b}, \overline{c}$ are non-coplanar vectors and $\lambda$ is a real number, then the vectors $\overline{a} + 2 \overline{b} + 3 \overline{c}, \; \lambda \overline{b} + 4 \overline {c}$ and $(2 \lambda -1) \overline{c}$ are non-coplanar for