x^4-x^3-2x^2+3x-1
=x^4-x^3-(2x^2-3x+1)
=x^3(x-1)-(x-1)(2x-1)
=(x-1)(x^3-2x+1)
=(x-1)(x^3-x^2+x^2-2x+1)
=(x-1)[x^2(x-1)+(x-1)^2]
=(x-1)^2(x^2+x-1)