Exception for Difference of squares

Math

\[a \cdot a - b \cdot b\]

C

double f(double a, double b) {
        double r8679 = a;
        double r8680 = r8679 * r8679;
        double r8681 = b;
        double r8682 = r8681 * r8681;
        double r8683 = r8680 - r8682;
        return r8683;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019191 +o rules:numerics
(FPCore (a b)
  :name "Difference of squares"

  :herbie-target
  (* (+ a b) (- a b))

  (- (* a a) (* b b)))

Backtrace

get-representation: Unknown representation #f		L	C
loop	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	122	4
prepare-points	/data/pavpan/nightlies/herbie/interface2/src/points.rkt	146	0
setup-prog!34	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	67	0
run-improve43	/data/pavpan/nightlies/herbie/interface2/src/mainloop.rkt	339	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.0/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.0/collects/racket/private/more-scheme.rkt	261	28