Polynomial factorisation

Hi,

consider this polynomial in x,y,p1,p2:

P = -4*y^2*p1^2*p2^2-4*y^3*p1*p2*x^3-4*y^5*p1*p2*x-y^4*x^6-2*y^6*x^4-y^8*x^2+4*a^2*p1^2+4*a^2*x^2*y^2

where

a is a (real or complex) constant.

I'm able to factorise this polynomial only with a=0. Can you find some other factorisation (I mean with a value of a =/= 0)?

Thanks, Nicola

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