Notation for "parallel" morphisms in a diagram Suppose $f\colon A\to B$ and $g\colon A\to B$ are possibly-distinct morphisms. How do I stick them both in a diagram (along with, e.g., their (co)equalizer) without suggesting that they are equal?
 A: Freyd and Ščedrov Categories, Allegories (Elsevier, 1990) use a "puncture mark" in a diagram to indicate this.

(Page 11.)
This covers your application as a special case.  For example, the definition of an equalizer involves $f,g: A\to B$ which are not necessarily equal, and $e: E\to A$ with $f\circ e = g\circ e$.  Freyd and Ščedrov represent this situation in the leftmost of the following set of diagrams:
 
(Page 42.)  The two arrows $A\to B$ have a puncture mark between, which removes the assertion of the arrows' equality that the diagram would normally be presumed to be requiring.  But since “the puncture mark removes only one equation”, equality of the two paths $f\circ e$  and $g\circ e$ is still asserted.
I don't know how widespread this notation is, however.
A: In simple cases (such as for (co)equalizers) you can get away with simply showing them beside each other. Even if you assert that the diagram commutes, that will not be understood as requiring equality between two morphisms that are explicitly shown and named in the diagram.
If the case is not simple, you can still draw the diagram (as an illustration of the situation) as long as you don't claim it commutes. You'll have to specify equations by saying that such-and-such specific subdiagrams commute.
... or perhaps it may be clearer just to duplicate an object in the diagram, such that the morphisms are not parallel anymore.
