In a tetrahedron \( ABCD \), let \( \vec{b} = \overrightarrow{AB} \), \( \vec{c} = \overrightarrow{AC} \), \( \vec{d} = \overrightarrow{AD} \), \( \vec{e} = \overrightarrow{AE} \) and \( \vec{f} = \overrightarrow{DE} \). Further let \( E \) be the midpoint of \( BC \). Express vectors \( \vec{e} \) and \( \vec{f} \) as a linear combination of vectors \( \vec{b} \), \( \vec{c} \), \( \vec{d} \).