Exception for 2sqrt (example 3.1)

Math

\[\sqrt{x + 1} - \sqrt{x}\]

C

double f(double x) {
        double r8619 = x;
        double r8620 = 1.0;
        double r8621 = r8619 + r8620;
        double r8622 = sqrt(r8621);
        double r8623 = sqrt(r8619);
        double r8624 = r8622 - r8623;
        return r8624;
}

Reproduce

Please include this information when filing a bug report:

herbie shell --seed 2019194 
(FPCore (x)
  :name "2sqrt (example 3.1)"

  :herbie-target
  (/ 1.0 (+ (sqrt (+ x 1.0)) (sqrt x)))

  (- (sqrt (+ x 1.0)) (sqrt x)))

Backtrace

result arity mismatch; expected number of values not received expected: 2 received: 1 in: local-binding form values...: 0		L	C
loop	/data/pavpan/nightlies/herbie/various-cleanup/src/core/extraction.rkt	25	2
(unnamed)	/data/pavpan/nightlies/herbie/various-cleanup/src/core/simplify.rkt	26	0
simplify!	/data/pavpan/nightlies/herbie/various-cleanup/src/mainloop.rkt	220	0
run-improve47	/data/pavpan/nightlies/herbie/various-cleanup/src/mainloop.rkt	342	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