Quotient of sum of exps

Specification

?
\[\begin{array}{l} \\ \frac{e^{a}}{e^{a} + e^{b}} \end{array} \]
(FPCore (a b) :precision binary64 (/ (exp a) (+ (exp a) (exp b))))
double code(double a, double b) {
	return exp(a) / (exp(a) + exp(b));
}
real(8) function code(a, b)
    real(8), intent (in) :: a
    real(8), intent (in) :: b
    code = exp(a) / (exp(a) + exp(b))
end function
public static double code(double a, double b) {
	return Math.exp(a) / (Math.exp(a) + Math.exp(b));
}
def code(a, b):
	return math.exp(a) / (math.exp(a) + math.exp(b))
function code(a, b)
	return Float64(exp(a) / Float64(exp(a) + exp(b)))
end
function tmp = code(a, b)
	tmp = exp(a) / (exp(a) + exp(b));
end
code[a_, b_] := N[(N[Exp[a], $MachinePrecision] / N[(N[Exp[a], $MachinePrecision] + N[Exp[b], $MachinePrecision]), $MachinePrecision]), $MachinePrecision]
\begin{array}{l}

\\
\frac{e^{a}}{e^{a} + e^{b}}
\end{array}

Reproduce

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herbie shell --seed 2023271 
(FPCore (a b)
  :name "Quotient of sum of exps"
  :precision binary64

  :herbie-target
  (/ 1.0 (+ 1.0 (exp (- b a))))

  (/ (exp a) (+ (exp a) (exp b))))

Please file a bug report with this information.

Backtrace

length: contract violation expected: list? given: 8000LC
(unnamed)/home/nightlies/herbie/arb-support/egg-herbie/main.rkt1112
egraph-run/home/nightlies/herbie/main/src/core/egg-herbie.rkt5020
egraph-run-rules/home/nightlies/herbie/main/src/core/egg-herbie.rkt5590
run-egg/home/nightlies/herbie/main/src/core/egg-herbie.rkt2880
simplify-batch/home/nightlies/herbie/main/src/core/simplify.rkt150
(unnamed)/usr/share/racket/collects/racket/contract/private/arrow-higher-order.rkt37933
find-preprocessing/home/nightlies/herbie/main/src/preprocess.rkt110
run-improve!/home/nightlies/herbie/main/src/mainloop.rkt3250
get-alternatives/report/home/nightlies/herbie/main/src/sandbox.rkt1490
(unnamed)/home/nightlies/herbie/main/src/sandbox.rkt2456
(unnamed)/usr/share/racket/pkgs/profile-lib/main.rkt4010
profile-thunk/usr/share/racket/pkgs/profile-lib/main.rkt90
(unnamed)/usr/share/racket/collects/racket/engine.rkt4224