The dimension of space-time can be declared directly - by command and the dimension itself may be an integer or an identifier: e.g. SPACEDIM N; - or indirectly - by declaring a Levi-Civita symbol (or tensor) by the number of its indices. It must be specified that the Weyl tensor can be introduced. If the dimension of space-time is declared then the metric tensor with contracted indices will be evaluated to the dimension itself automatically during the simplification of tensor expressions.
The signature of the metric tensor can be given by the command
SIGNATURE and may be an integer or an identifier, e.g. SIGNATURE M;.
The signature and dimension are needed in order that the switch
LEVI!-CIVITA will work (see page 
).
If both the dimension of
space-time and the signature of the metric tensor are numbers, then the
system also checks their compatibility. Both quantities can be redefined by
declaring them with new values or can be removed from the system by the
commands
