Let \( \vec{a} = 2\hat{i} + \hat{j} - \hat{k}, \ \vec{b} = \big((\vec{a} \times (\hat{i} + \hat{j})) \times \hat{i}\big) \times \hat{i} \). Then the square of the projection of \( \vec{a} \) on \( \vec{b} \) is:
\( 2 \)
\( \frac{2}{3} \)
\( \frac{1}{5} \)
\( \frac{1}{3} \)