A formula is any arithmetic expression which may contain all variables and
functions known to the system.
The result of a formula may be taken as input for all parameters for which a
numerical value is permitted.
If it is possible to save a constructional relation under a certain command,
you may control with the help of rule 8 whether the formula is saved as
such or only as the current value of it. This is decisive for the future
behavior of SISCAD-P.