Math & Science ⇒ syntax for a double headded arrow for exact sequences

[mrotsliah]

Using the empheq package, I can use the syntax \xhookrightarrow{f\circ g} for a right arrow with a hook on the left of the arrow to indicate that that map is an injection. This arrow also has f\circ g above it. What is the syntax for a right arrow with a double head on the right to indicate a surjective map? That is, something along the lines of \xrightarrowdoublehead{h\circ k}.

Thanks

[frabjous]

That command does not come from the empheq package, it comes from the mathtools package, though I can understand the confusion since the empheq package automatically loads the mathtools package.

Anyway, look at page 11 of the mathtools documentation or better yet, the Comprehensive LaTeX symbol list (pp. 69-70 in the letter paper version) for the arrow that suits your needs.

You might also try drawing the symbol in DeTeXify.

It wasn't obvious to me what you needed. Maybe \xtwoheadrightarrow{f\circ g} from the extpfeil package,

[mrotsliah]

I can cheat. I discovered this by accident.

\xrightarrow{h\circ k}\!\!\!\!\to

[frabjous]

Your cheat looks better than I might have guessed, but yeah, \xtwoheadrightarrow{f\circ g} from the extpfeil package is the more ordinary way of getting what you want.

[mrotsliah]

Sweet. Thank you very much.