SafeDollar ‘stablecoin’ drops to $0 following DeFi exploit on Polygon

Re:SafeDollar ‘stablecoin’ drops to $0 following DeFi exploi... by theli0nheart on Tuesday June 29, 2021 @11:51AM (#27677648)

Let's formalize this to make it easier to discuss.

  𝐏(𝐀)  = 𝐏(contract has been hacked)
  𝐏(¬𝐀) = 𝐏(contract has not been hacked)
  𝐏(𝐁)  = 𝐏(contract is hack resistant)

Relevant conditional probabilities:

  𝐏(𝐁|¬𝐀) =
    𝐏(contract is hack-resistant given that it has not been hacked)
  𝐏(¬𝐀|𝐁) =
    𝐏(contract has not been hacked given that it is hack-resistant)

The fallacy of the inverse would be assuming that:

> The probability that a contract is hack-resistant, given that it has not been hacked, is approximately equal to the probability that it has not been hacked, given that it's hack resistant.

More succinctly:

  𝐏(𝐁|¬𝐀) ≅ 𝐏(¬𝐀|𝐁)

In https://news.ycombinator.com/item?id=27666484, the fallacy of the inverse was presented as "those contracts not being hacked yet is no proof that they are resistant to hacks" or "NOT (NOT A implies B)", i.e.:

  ¬(¬𝐀 → 𝐁)

In summary:

  𝐏(𝐁|¬𝐀) ≅ 𝐏(¬𝐀|𝐁) => the fallacy of the inverse

    and

  ¬(¬𝐀 → 𝐁)         => statement in comment

These two statements are fundamentally different.

Note that the first statement is a comparison of probabilities, and the second is not. They're not the same. There might be another fallacy at play here, but it's not the fallacy of the inverse.

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Re:SafeDollar ‘stablecoin’ drops to $0 following DeFi exploi... by Closi on Wednesday June 30, 2021 @12:29AM (#27684872)

To be honest, I don’t fully follow the above, and I’m not sure if this formalises the same problem. Copying the definition from Wikipedia:

> If P, then Q.

> Therefore, if not P, then not Q.

In this case, we could plug in the below values:

P = Contract Hacked Q = Insecure

I.e. if the contract has been hacked the code was insecure. Therefore if the contract has not been hacked, it is not insecure.

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