The cases where no definite article is needed

In technical writing, I believe expressions like these do not require a definite article:

• Function f(x) is such and such. Graph G has such property. Equation (10) combined with something else gives that.

I mean one should not (or need not?) say "the function f(x)", "the graph G", "the equation (10)", etc..

This is my recollection from what a copy editor did to my writing a long time ago. Is this impression correct? If so, what is the name of this rule? I mean how can I refer others to this point?

Solution 1:

That is my impression as well. As for the rule, it's because an article is not necessary before proper nouns. In your examples, Function f(x), Graph G, and Equation 10 are all proper nouns, having names f, G, and 10 respectively.