\eagle\x-ray-fish\octopus\boar\rat\shrimp { \lambda } _ { { \mu } { \nu } } ( x ) \equiv \frac { { \partial } _ { \mu } a ( x ) { \partial } _ { \nu } a ( x ) } { { \partial } _ { \eta } a ( x ) { \partial } ^ { \eta } a ( x ) } ,