Function gauss_three_multiply_identity 

pub fn gauss_three_multiply_identity() -> bool

Gauss’s three-multiplication identity — the symmetry that turns a 4-multiply bilinear form ad + bc into 3 multiplies (a+b)(c+d) − ac − bd. It is the archetypal “spend an add to save a multiply” rewrite behind fast complex / polynomial / NTT-butterfly multiplication. Certified as a polynomial identity over any commutative ring by the kernel’s ring canonicalizer, so a codegen pass may apply it knowing it is sound.