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Algorithm Explanations

totalDollars is the total dollar value required to be raised in the Barn Raise. It is equal to dollarPerUnripeLP() * unripeLP().totalSupply(). If no Farmer has forfeited Unripe LP, then totalDollars is 77 million, but given that Farmer's can chop their Unripe LP and forfeit the funds they have not yet been paid back, we need totalDollars to decrease with the total supply of Unripe LP.
if (s.recapitalized >= totalDollars) return 0; —
A safe guard in case Beanstalk ends up in a situation where too much is raised. This is also possible if someone uses the chop function at a penalty even after the full amount has been raised.
return totalDollars.sub(s.recapitalized); —
s.recapitalized is incremented every time USDC is exchanged for Fertilizer (or Unripe LP is generated through Convert), but it is equal to the dollar value that has been recapitalized. Thus, the difference between the two is the amount remaining.

​checkForMaxDeltaB​

See EBIP-2.
It is assumed that if |deltaB| > beanSupply / 100, then manipulation occurred. This isn't always true, but the ramifications if |deltaB| > beanSupply / 100 naturally are minimal as Beanstalk will simply mint fewer Beans/less Soil this Season.
Theoretically, a multi-block MEV attack could manipulate deltaB to be any value. Multi-block MEV can only be executed on some time cadence dependent on % ownership of Ethereal stake. Therefore, the greatest vulnerability to Beanstalk is a massive one-time Bean/Soil issuance. By adding this supply cap, the maximum effect of potential manipulation can be at most 1% of supply.