Mars4 ERC20

As it presently is constructed, the contract is vulnerable to the [allowance double-spend exploit](https://github.com/OpenZeppelin/openzeppelin-solidity/blob/b4f87bb8fc25fb07f73099701e39e167a3d36465/contracts/token/ERC20/ERC20.sol#L71-L78), as with other ERC20 tokens.

The clone-and-own approach involves copying and adjusting open source code at one's own discretion. From the development perspective, it is initially beneficial as it reduces the amount of effort. However, from the security perspective, it involves some risks as the code may not follow the best practices, may contain a security vulnerability, or may include intentionally or unintentionally modified upstream libraries. Rather than the clone-and-own approach, a good industry practice is to use the Truffle framework for managing library dependencies. This eliminates the clone-and-own risks yet allows for following best practices, such as, using libraries.

A greedy contract is a contract that can receive ether which can never be redeemed.

A block is an ordered collection of transactions from all around the network. It's possible for the ordering of these transactions to manipulate the end result of a block. A miner attacker can take advantage of this by generating and moving transactions in a way that benefits themselves.

Every Solidity file specifies in the header a version number of the format `pragma solidity (^)0.4.*`. The caret (`^`) before the version number implies an unlocked pragma, meaning that the compiler will use the specified version _and above_, hence the term "unlocked".