Bignum: natural subtraction sometimes wrong
Consider
module Main (main) where
import Numeric.Natural
main :: IO ()
main = print (n - s)
where
n, s :: Natural
n = 137503105969312982142385040956303729937425409769904987267247644890331944583201
s = 370814112419299627365008243601943822482
Compiled with HEAD it prints 0.