# Assumption that a parameter is real [duplicate]

I'm making some calculations, where I use the command Conjugate[f[x]]. In the function f[x] appears a parameter J, which is Real. How can say mathematica that it should not take the Conjugate of J?

So, I would like to say mathematica that J is real. I tried to write

Assumptions -> J e Reals

in the beginning of the code, but it doesnt work.

Ideas?

Best

• If you really want to set the assumption globally for the session, then look up \$Assumptions in the documentation. – MarcoB Nov 8 '15 at 16:02
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    Refine[Conjugate[f[x]], J \[Element] Reals]