I am currently revising a paper and I am completely confused about the commas. Is it correct English to write
1) "The canonical map $X \to Y$, $x \mapsto f(x)$, is injective."
or is it
2) "The canonical map $X \to Y$, $x \mapsto f(x)$ is injective." ,
i.e. is the second comma mandatory, optional or wrong?