I know that I asked similar questions in the past, but I still do not seem to figure it out, what the best way is to post a 'complex' diagram on this website.

Nothing seems to work, and the things that do work aquire a lot of work and take to much time in my opinion...

I just posted this question: Universal property of product topology, unique up to homeomorphism

Which was not fun at all. Can you please tell me, how I could have drawn these diagrams here with the most efficient method?

Thank you!

  • 5
    $\begingroup$ See also: How to draw a commutative diagram? If you know xypic syntax, you could use presheaf for the type of diagrams in the linked post: Challenge: can you draw the following triangular diagram? and Triangle commutative diagram does not work here at MO. $\endgroup$ Commented Aug 20, 2019 at 3:58
  • 1
    $\begingroup$ The limited $\LaTeX$ implementation here for MathJax purposes is likely a factor in the difficulty of drawing such diagrams. See the numerous posts on this subject at TeX.SE, e.g. Drawing a commutative diagram. If you do a fair amount of these, esp. more complicated ones, then a standalone implementation with tikz-cd might be worth the learning curve (to prepare images for uploading). $\endgroup$
    – hardmath
    Commented Aug 20, 2019 at 23:30
  • $\begingroup$ Technically MathJaX is an AJAX( javascript engine) library, with LaTeX style commands. But I agree with @hardmath That learning a LaTeX package or two to upload clean images. might go a long way. $\endgroup$
    – user645636
    Commented Aug 20, 2019 at 23:45

1 Answer 1


$$\underset{\underset{\hspace{-20px}l_k}\searrow}{y\overset{f}\longrightarrow}\underset{\hspace{-20px}X_{l_K}}{\underset{\downarrow P_{r_k}}{\hspace{-20px}X}}$$
I mostly used underset and overset:

\underset{\underset{\hspace{-20px}l_k}\searrow}{y\overset{f}\longrightarrow}\underset{\hspace{-20px}X_{l_K}}{\underset{\downarrow P_{r_k}}{\hspace{-20px}X}}

Might be able to use stackrel after grouping the main line, or getting the arrows longer by requiring an extended arrow package. Could define the triangle with optional arguments to fill in.

  • 3
    $\begingroup$ Thank you, but this looks terrible. :) Well... better then my awful hand drawings. $\endgroup$
    – Cornman
    Commented Aug 20, 2019 at 16:45
  • $\begingroup$ it's the ahort arrows below. without using style to rotate them, or extendible arrows, I'm no expert. $\endgroup$
    – user645636
    Commented Aug 20, 2019 at 18:14
  • $\begingroup$ math.meta.stackexchange.com/a/16888/645636 @Cornman $\endgroup$
    – user645636
    Commented Sep 13, 2019 at 21:45

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