Let be a metric on a 4-dimensional manifold with signature A null vector satisfies

Let  be a solder form for the metricthat is,  is a rank 3 spin-tensor such that  The NullVector command accepts, as its first argument, a solder form with either covariant or contravariant tensor and spinor indices.

With two arguments, the NullVector command returns the real vector with components

This command is part of the DifferentialGeometry:-Tensor package, and so can be used in the form NullVector(...) only after executing the commands with(DifferentialGeometry); with(Tensor) in that order.  It can always be used in the long form DifferentialGeometry:-Tensor:-NullVector.