Definite article in Maths: "(the) function f"

Is the definite article correct/necessary in sentences like the following?

A line that intersects (the) circle C.
We can see that (the) function f has a maximum at x=0.

Draw a line past (the) edge E. 

I am aware that definite articles must not be used in things like "in Figure 3" or "see Equation 7", because here "Figure" and "Equation" are treated as proper nouns (and thus capitalized). But in other kind of sentences as the previous ones, I am unsure about whether it is also correct to omit the definite article or not.