I'd like to render the string Id as a Math Operator in upright boldface. What is the proper markup for that? \mathbf{\operatorname{Id}}? \operatorname{mathbf{Id}}? \mathop{\mathbf{Id}}?

Note; this is for code in a macro, not inline.

  • 3
    – egreg
    Jun 27, 2019 at 15:06

1 Answer 1





$\mathbf{\operatorname{Id}}$ is wrong

$\operatorname{\mathbf{Id}}$ seems good

$\mathop{\mathbf{Id}}$ seems good

$\displaystyle\operatorname{\mathbf{Id}}_{X}$ seems good

$\displaystyle\mathop{\mathbf{Id}}_X$ is wrong


enter image description here

Thus the right one is \operatorname{\mathbf{Id}}. Of course, if you use it more than a couple of times, you should do


in your document preamble and use \Id.

  • This is for a macro, not inline. I've edited the question to clarify that.
    – shmuel
    Jun 27, 2019 at 18:18
  • Why should \operatorname{\mathbf{Id}} be preferred to \mathop{\mathbf{Id}}?
    – Patricio
    Mar 2 at 13:40
  • @Patricio Try \mathop{\mathbf{x}}
    – egreg
    Mar 2 at 16:07
  • I just have, but I'm unable to tell the difference.
    – Patricio
    Mar 3 at 7:12
  • Now I see, it's its handling of subindices in displays, isn't it? Sorry for bothering you with this
    – Patricio
    Mar 3 at 7:14

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