Toolkit 23

SFFT (Simon's Favorite Factoring Trick)

xy+ax+by=c    (x+b)(y+a)=c+abxy+ax+by=c\;\Rightarrow\;(x+b)(y+a)=c+ab
GSFFT (General Form)\text{GSFFT (General Form)}
axy+bx+cy=daxy+bx+cy=d
a2xy+abx+acy=ada^2xy+abx+acy=ad
(ax+c)(ay+b)=ad+bc(ax+c)(ay+b)=ad+bc