| \eta _ { 4 } | = h _ { [ 0 ] } ^ { 2 } \frac { b ( \lambda ) } { \sin ^ { 2 } \theta a ( \lambda ) } \left [ \left ( \omega ^ { - 1 } ( x ^ { i } , v ) \right ) ^ { \ast } \right ] ^ { 2 } ,  \elephant\hawk