19. Ethereum RLP: https://github.com/ethereum/wiki/wiki/%5BEnglish%5D-RLP 20. Ethereum Merkle Patricia trees: https://github.com/ethereum/wiki/wiki/%5BEnglish%5D-Patricia-Tree 21. Peter Todd on Merkle sum trees:http://sourceforge.net/p/bitcoin/mailman/message/31709140/ Page 36 ethereum.org
Ethereum White Paper by Vitalik Buterin Page 41 Page 43