# 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

## marked as duplicate by MarcoB, user9660, Jens, dr.blochwave, LLlAMnYPNov 9 '15 at 8:36

• 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
    Refine[Conjugate[f[x]], J \[Element] Reals]