// ### for deposits: d1, d2, d3, the beneficiary are: c1, c2, c2
    depositAmount          claimerShares
d1: + 100e18           c1: + 100e36
d2: + 100e18           c2: + 100e36
d3: + 100e18           c2: + 100e36

depositAmount of d1, d2, d3 = 100e18
c1 claimerShares: 100e36
c2 claimerShares: 200e36
total shares: 300e36


// ### when the PPS of AUST drop by 50% 
totalUnderlyingMinusSponsored: 300e18 -> 150e18

// ### d2 withdraw
c2 claimerShares: 200e36
d2 depositAmount: 100e18
d2 depositShares: 300e36 * 100e18 / 150e18 = 200e36

Shares to reduce: 200e36
c2 claimerShares: 200e36 -> 0
c2 totalPrincipal: 200e18 -> 100e18
totalShares: 300e36 -> 100e36

underlying.safeTransfer(d2, 100e18)
totalUnderlyingMinusSponsored: 150e18 -> 50e18
adjustedUnderlying = underlying + totalLoss
