</span> c: ⎡x₁  x₃⎤</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎢      ⎥</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎢x₁  x₄⎥</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎢      ⎥</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎢x₁  x₃⎥</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎢      ⎥</span>
<span class="r-out co"><span class="r-pr">#&gt;</span>    ⎣x₁  x₄⎦</spa