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I want the following lemma:

Given k\"ahler metric $g_{\al \overline{\be}}$ with associated Ricci curvature $ \text{Ric} =R_{\al \overline{\be}}$ the Ricci form defined by 
\begin{equation*} 
\p (X,Y) = \frac{1}{2} \text{Ric} (J X, Y)
\end{equation*}
we have the following local expression ...

The problem is that I like to have the statement of my lemmas to be in italics, but in this case the \text{...} command I use to write the Ricci curvature (ie \text{Ric}) puts Ric in italics and not plain text, I do not know how to rectify this?

By the way the command I use to set up my lemma is:

\newtheorem{lem}{Lemma}[section]

P.S. sorry for how badly formatted this question is but my LaTeX is quite poor.

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  • 8
    Ric is a math operator and should not be typeset with \text, that command us solely for textual comments. Use \operatorname if it is a one of, or use \DeclareMathOperator{\Ric} {Ric} if it is used often. This \text misuse is seen quite often
    – daleif
    Commented Dec 20, 2015 at 13:35
  • 1
    @daleif An answer, please.
    – egreg
    Commented Dec 20, 2015 at 17:19

1 Answer 1

8

It is a very commonly seen error to use \text in this way. But \text is for textual comments only, it switches to the text font and the current font shape (as you mentioned).

Ric on the other hand is a mathematical operator and should be typeset, upright, in the current math font + have operator status.

For a one of you can use: \operatorname{Ric} , but it is often better to simply define a \Ric operator via

\DeclareMathOperator\Ric{Ric} 

And then use that. This also have the added bonus of a cleaner math code.

If Ric is not an operator, you can just use \mathrm{Ric} as a one off, or

\newcommand\Ric{\mathrm{Ric}}

for getting it as a macro (thanks to Willie for that comment)

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  • It is much more common to use \mathrm{Ric} instead, FWIW. (Most geometers would not consider it an operator.) Commented Dec 22, 2015 at 3:57
  • @WillieWong added
    – daleif
    Commented Dec 22, 2015 at 12:07

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