The following structure is used to define a law without a spine.

Note for all character string values in the structure, if the character
string is in expression format (e.g., p5=25, p5+p7), and the
expression does not exist, an expression is created and the law is
associated to that expression. If the expression does exist, then the
existing expression is edited, and the law is associated to that
expression. If the character string contains an expression name (e.g.,
p5) and the expression exists, the law is associated to that expression,
if the expression does not exist an error occurs. If the character string
is a numeric value (e.g., 25) the law is not associated to an expression.

When a function is returning the law structure for a particular
parameter, all character string values are fully defined expressions
(i.e., p5=25), if they had an associated expression