Find a linearly independent set of vectors that spans the same subspace of ${\mathbb R}^4$ as that spanned by the vectors $$\left[\begin{array}{c} -6\cr 4\cr 4\cr 0 \end{array}\right], \ \ \ \ \left[\begin{array}{c} 1\cr 0\cr -1\cr 2 \end{array}\right], \ \ \ \ \left[\begin{array}{c} 1\cr -2\cr -3\cr 5 \end{array}\right], \ \ \ \ \left[\begin{array}{c} -2\cr 2\cr 2\cr -1 \end{array}\right].$$ A linearly independent spanning set for the subspace is: