Three principal invariants with respect to this quantity are named for Chern-Pontryagin, Euler, and Kretschmann. A renormalization method named for this quantity is used to find the order parameter of topological phase transitions. Non-zero values of this quantity necessitate generalizing the derivative operator to the (*) covariant derivative. (10[1])The affine (10[1])connections vanish for systems (10[1])in which this quantity is equal to zero. (-5[1])The contracted Bianchi identity relates a tensor and a scalar describing this property, both (10[1])of which are named for Ricci. (10[1])Non-zero values of this quantity cause gravitational lensing, or the bending of light. (-5[1])When this quantity is non-zero, straight lines are generalized into geodesics. For 10 points, what quantity is zero for flat spacetime? ■END■ (10[1]0[1])