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### Solidity: Deposit/Withdraw Asymmetry Example

Source: https://evmresearch.io/security-patterns/complementary+function+pairs+that+don't+mirror+all+state+mutations+may+have+an+asymmetry+bug

This Solidity code demonstrates an asymmetry bug where the `deposit` function sets an `isActive` flag, but the `withdraw` function forgets to unset it. This can lead to unexpected contract states.

```solidity
function deposit(uint id) external {
    balances[id] += msg.value;
    isActive[id] = true;  // set
}
function withdraw(uint id) external {
    balances[id] = 0;
    // isActive[id] = false;  // forgotten — asymmetry bug
}
```

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