Vault Account
The Vault Account is a struct used for accounting in the Fraxlend Pair:
struct VaultAccount {
uint128 amount;
uint128 shares;
}
The Vault Account contains two elements:
  1. 1.
    amount - represents a total amount
  2. 2.
    shares - represents claims against the amount

In lending, amount represents the total amount of assets deposited and the interest accrued.
When lenders deposit assets, the amount of assets deposited increases amount, the shares value is also increased by an amount such that the ratio between amount/shares remains unchanged.
When interest is accrued, amount is increased and shares remains the same. Each lender's share of the underlying assets are measured in shares.
When lenders remove liquidity, they redeem shares for the underlying asset. The shares amount will be decreased by the number of shares redeemed, the amount will be decreased such that the ratio between amount/shares remains unchanged.
Borrow Accounting
In borrowing, amount represents the total amount of assets borrowed and the interest accrued.
When borrowers receive assets, the number of tokens received increases amount, the shares value is also increased by an amount such that the ratio between amount/shares remains unchanged.
When interest is accrued, amount is increased and shares remains the same. Each borrower's debt is measured in shares.
When borrower's repay debt, amount is decremented by the amount of assets returned, shares is decreased by an amount such that the ratio of amount/shares remain unchanged. An individual borrowers shares balance is decremented by this number of shares.
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