# New symbol for an exact sequence

A sequence $A\to B \to C$ is exact if $\operatorname{im} f = \ker g$, where $f:A\to B$ and $g:B\to C$.

Why is there not a symbol to denote such a sequence? Which one would you suggest?

• What is f? What is g? – Michał Zapała Sep 19 '18 at 21:45
• also please consider using MathJax – Michał Zapała Sep 19 '18 at 21:45
• Because nobody thought it necessary. – egreg Sep 19 '18 at 22:02
• I just write $(ex)$ at the beginning/end of the exact row/column.. – Berci Sep 19 '18 at 22:22
• I prefer using the words "is exact" after the diagram. Or "the exact sequence" before the diagram. – GEdgar Sep 20 '18 at 0:16

So I would suggest to just write «this sequence is exact at $B$», or that «pair of morphisms $f, g$ is exact» (which is better, in my opinion).
• Not to rant, but I HATE seeing arguments written out in logical symbols. "Oh, the proof is clear. Just note that $\neg((\nexists x \in P \forall y \in Z \ni x \notin W(\alpha) \vee y) \Rightarrow (J \Leftrightarrow K \wedge Q)$." – Randall Sep 20 '18 at 14:56