Exception for 2atan (example 3.5)

Math

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

C

double f(double N) {
        double r15383 = N;
        double r15384 = 1.0;
        double r15385 = r15383 + r15384;
        double r15386 = atan(r15385);
        double r15387 = atan(r15383);
        double r15388 = r15386 - r15387;
        return r15388;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019315 +o rules:numerics
(FPCore (N)
  :name "2atan (example 3.5)"
  :precision binary64

  :herbie-target
  (atan (/ 1 (+ 1 (* N (+ N 1)))))

  (- (atan (+ N 1)) (atan N)))

Backtrace

argmin: contract violation expected: (and/c list? (not/c empty?)) given: '() argument position: 2nd other arguments...: #<procedure:composed>		L	C
argmin	/opt/racket-7.2/collects/racket/list.rkt	765	0
infer-splitpoints	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/core/regimes.rkt	34	0
get-final-combination	/data/pavpan/nightlies/herbie/fix-interface-bugs/src/mainloop.rkt	370	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28
run	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	39	2
profile-thunk16	/opt/racket-7.2/share/pkgs/profile-lib/main.rkt	9	0
(unnamed)	/opt/racket-7.2/collects/racket/private/more-scheme.rkt	261	28