Origin X

The implementation of the `isContract` check can not cover all scenarios. The check can be bypassed if the call is from the constructor of a smart contract or when the contract is destroyed. Because, in that case, the codesize will also be zero. The "isContract" function in the OpenZeppelin "Address" library uses the same implementation, but comments mention that "it's unsafe to rely on the check and it can be bypassed". Reference: https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Address.sol

`claimOpenTime` value is set to 0 initially, which is value that could make the `require()` check in L298 and L311 passed in any situation.

The given input `superior` in the function `pay()` is missing the check for the non-zero address.

Solidity version >=0.8.0 includes checked arithmetic operations and underflow/overflow by default, making SafeMath redundant.

The contract has unlocked compiler version. An unlocked compiler version in the source code of the contract permits the user to compile it at or above a particular version. This, in turn, leads to differences in the generated bytecode between compilations due to differing compiler version numbers. This can lead to an ambiguity when debugging as compiler specific bugs may occur in the codebase that would be hard to identify over a span of multiple compiler versions rather than a specific one.

The linked variables could be declared as `constant` since these state variables are never modified.

The linked variables assigned in the constructor can be declared as `immutable`. Immutable state variables can be assigned during contract creation but will remain constant throughout the lifetime of a deployed contract. A big advantage of immutable variables is that reading them is significantly cheaper than reading from regular state variables since they will not be stored in storage.