This is just a warning for readers of the Stacks project: please be careful as I think I don’t know left from right. As a consequence, the text of the Stacks project sometimes uses the phrase “section” when it should be using “retraction”. Similarly, watch out for confusion between “left inverse” and “right inverse”.

If you find occurrences of this, just leave a comment to point it out and we’ll fix it.

Thanks!

In the Roman alphabet, r precedes s. So when I explain “splitting” of a short exact sequence in an algebra course, I draw the dashed arrow for r (retraction) to the left of the dashed arrow for s (section). Unfortunately, also p precedes q, and I always use q for the monic term in the short exact sequence, and p for the epic term in the short exact sequence. So the alphabet trick is not very consistent.

Hilarious!