Exception for 2atan (example 3.5)

Math

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

C

double f(double N) {
        double r10040878 = N;
        double r10040879 = 1.0;
        double r10040880 = r10040878 + r10040879;
        double r10040881 = atan(r10040880);
        double r10040882 = atan(r10040878);
        double r10040883 = r10040881 - r10040882;
        return r10040883;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019173 
(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

hash-ref: no value found for key key: #<enode 166(166)>		L	C
for-loop	/data/pavpan/nightlies/herbie/various-cleanup/src/core/simplify.rkt	197	2
extractor-extract	/data/pavpan/nightlies/herbie/various-cleanup/src/core/simplify.rkt	196	0
for-loop	/data/pavpan/nightlies/herbie/various-cleanup/src/core/simplify.rkt	35	2
(unnamed)	/data/pavpan/nightlies/herbie/various-cleanup/src/core/simplify.rkt	26	0
simplify!	/data/pavpan/nightlies/herbie/various-cleanup/src/mainloop.rkt	217	0
run-iter!	/data/pavpan/nightlies/herbie/various-cleanup/src/mainloop.rkt	320	0
for-loop	/data/pavpan/nightlies/herbie/various-cleanup/src/mainloop.rkt	354	4
run-improve43	/data/pavpan/nightlies/herbie/various-cleanup/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