Question: expand multivariate polynomial

Hi, all, I have a question, how to expand a multivariate polynomial, like this: F := [1-(x[1]-1)^2]*[1-(x[3]-1)^2]+[1-(x[1]-1)^2]*[1-(x[2]-2)^2]+(2*[1-(x[1]-1)^2])*[1-(x[2]-2)^2]*[1-(x[3]-1)^2] when I used expand(F); the result is the same as F itself, nothing changed. Whether there is some way to expand the multivariate polynomial into a completely expanded form, like: 2*x*y^2*z^2+2*x*y^2*z+x*y*z^2+x*y*z+x^2*z^2+x^2*z+x*z^2+x*z+x^2*y^2+2*x^2*y+x*y^2+2*x*y thanks.
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