Testing whether a document has option "fleqn"

Hefferon, Jim S. jhefferon at smcvt.edu
Sat May 4 00:30:49 CEST 2019

How can I test whether the document has the class option `fleqn`?  I want to have an environment that takes the place of center but that if required gives content that is left-aligned, as equations are left-aligned under fleqn.

I had in mind something like this.  However this one gives `! LaTeX Error: Can be used only in preamble.`  

      \trivlist \item \relax \hspace*{\mathindent}
      \trivlist \centering \item \relax

I know that there are flags like \@fleqntrue and have spent some time trying toggle commands, etc, but been unable to hit on the right one.  A tip would really help me.

Thank you,

... those dreadful hammers!
  --John Ruskin, 1851

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