One of the rule for symbols is that it should be very unique. The other rule is that is should not be an exact copy of the other already used symbols.
Rule frequently expressed in statistical symbols?
Rule or principle frequency expressed in statistical symbols?
formula
Formula
I believe it is formula.
A mathematical rule can be called many things including a theory. Proofs can prove this theory to be a rule.
formula
tacos are delicious
various arrows
differ proper names from things named after proper names
It set an example for self-rule.
A rule is a way of describing a function in words. Conversly, a function is simply a way of describing mathematical rules in numbers and symbols.