Using h to denote the gravitational potential, the Lagrangian for the graviton has terms proportional to h, h cubed, and h times this operation applied to h. This operation's associated Green's function equals a delta function of “t minus r over c” divided by 4 pi r. In the Lorenz gauge, applying this operation to the vector potential gives negative mu-nought (-5[1])times the current density. This (*) Lorentz-invariant operation (-5[1])is applied to a function to give zero in the most compact representation of the wave equation. (10[1])It is defined as one over c squared times the second time derivative, minus the square of the gradient. Either a box or “box squared” symbolizes, for 10 points, what operation named for a French physicist, the analogue of the Laplacian in Minkowski space? (10[1])■END■