Exception for 2atan (example 3.5)

Math

\[\tan^{-1} \left(N + 1\right) - \tan^{-1} N\]

C

double f(double N) {
        double r8310 = N;
        double r8311 = 1.0;
        double r8312 = r8310 + r8311;
        double r8313 = atan(r8312);
        double r8314 = atan(r8310);
        double r8315 = r8313 - r8314;
        return r8315;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019191 
(FPCore (N)
  :name "2atan (example 3.5)"

  :herbie-target
  (atan (/ 1.0 (+ 1.0 (* N (+ N 1.0)))))

  (- (atan (+ N 1.0)) (atan N)))

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