1. Etherscan.
https://etherscan.io
2. Smtchecker documentation.
https://solidity.readthedocs.io/en/v0.6.6/security-considerations.html#formal-verification
3. Solidity documentation.
https://solidity.readthedocs.io
4. theDAO.
https://etherscan.io/address/0xbb9bc244d798123fde783fcc1c72d3bb8c189413
5. Vyper documentation.
https://vyper.readthedocs.io