A cura di: Alfredo Bochicchio

$a^8-2a^4b^4+b^8-c^4$
$(a^4-b^4)^2-c^4$
$(a^4-b^4)^2-(c^2)^2$
$(a^4-b^4-c^2)(a^4-b^4+c^2)$