Talk:D'Alembert operator
Is is written or ?
It is equal to <math>\nabla^2 - \frac{1}{c^2} \frac{\partial^2}{\partial t^2}<\math> or <math>\frac{1}{c^2} \frac{\partial^2}{\partial t^2} - \nabla^2<\math>? Sources differ again.
Is is written 
It is equal to <math>\nabla^2 - \frac{1}{c^2} \frac{\partial^2}{\partial t^2}<\math> or <math>\frac{1}{c^2} \frac{\partial^2}{\partial t^2} - \nabla^2<\math>? Sources differ again.