function of negative x

[mgalasi (Massimo Galasi)]

Hi all mathematica staff

I have this function:

B(x)=(1-x^2-4x^3+6x^4)/((1-2x-x^x)(1-x))

And I want this:

B(-x)

How can I obtain the solution?

Thanks

[gianlucagorni]

B[x_] := (1 - x^2 - 4 x^3 + 6 x^4)/((1 - 2 x - x^x) (1 - x));
B[-x]