# How to use assumptions without Simplify[]? According to this simple example program, the assumptions evaluated only with the Simplify[] function call. However, I wouldn't like to use Simplify[] because it can be very slow with longer expressions.

I would like the Conjugate[c10] function call to give me the c10 output after the assumption is defined. Is there a way to do this?

ClearAll["Global*"]

$$Assumptions := True Conjugate[c10] Refine[Conjugate[c10]] Simplify[Conjugate[c10]]$$Assumptions

$$Assumptions := c10 \[Element] Reals Conjugate[c10] Refine[Conjugate[c10]] Simplify[Conjugate[c10]]$$Assumptions

ClearAll["Global*"]
$Assumptions  ## 1 Answer You could Unprotect Conjugate to get the behavior you want, although it will undoubtedly slow down computations involving Conjugate: SetConjugateSimplification[bool_] := ( Unprotect[Conjugate]; If[TrueQ @ bool, Conjugate[e_] /; !TrueQ@$$Flag := Block[{$$Flag=True}, Simplify @ Conjugate[e]], DownValues[Conjugate] = {} ]; Protect[Conjugate]; )  Then, turn on conjugate simplification: SetConjugateSimplification[True]  Now, Conjugate will use assumptions specified with $Assumptions or Assuming:

\$Assumptions = c10 ∈ Reals;
Conjugate[c10]


c10

Restore the usual Conjugate behavior:

SetConjugateSimplification[False]


Another possibility is to use UpValues:

c10 /: Conjugate[c10]:= c10


Then:

Conjugate[c10]
Conjugate[c10+x]
Conjugate[Exp[c10 x]]


c10

c10 + Conjugate[x]

E^(c10 Conjugate[x])