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Match a protective put with call plus terminal cash

Stock plus a strike-100 put and a strike-100 call plus certain terminal 100 both pay max(S,100).

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State the two compatible packages

Package A contains one underlying unit and one strike-100 put. Package B contains one strike-100 call and a certain cash amount 100 due at the same expiry. The table concerns terminal amounts, not present purchase costs.

Calculate each package

Below 100, A adds S and 100−S while B has zero call payoff plus 100. Above 100, A is S while B adds S−100 and 100. They match at every nonnegative terminal price.

Inspect the original scenarios

Original replication table
Terminal priceStock plus putCall plus terminal cash
0100100
80100100
100100100
120120120
150150150

Discount the cash only when changing dates

To compare present costs under the selected European/no-income assumptions, the terminal cash amount becomes 100D today. Using undiscounted 100 as its present cost mixes dates unless D=1. The payoff identity itself needs no such discount calculation.

Further references