Literature Review: Smart Contract Semantics <s> Defeasible Logic <s> We often reach conclusions partially on the basis that we do not have evidence that the conclusion is false. A newspaper story warning that the local water supply has been contaminated would prevent a person from drinking water from the tap in her home. This suggests that the absence of such evidence contributes to her usual belief that her water is safe. On the other hand, if a reasonable person received a letter telling her that she had won a million dollars, she would consciously consider whether there was any evidence that the letter was a hoax or somehow misleading before making plans to spend the money. All to often we arrive at conclusions which we later retract when contrary evidence becomes available. The contrary evidence defeats our earlier reasoning. Much of our reasoning is defeasible in this way. Since around 1980, considerable research in AI has focused on how to model reasoning of this sort. In this paper, I describe one theoretical approach to this problem, discuss implementation of this approach as an extension of Prolog, and describe some application of this work to normative reasoning, learning, planning, and other types of automated reasoning. <s> BIB001 </s> Literature Review: Smart Contract Semantics <s> Defeasible Logic <s> In this paper we present an architecture to represent and reason on e-Contracts based on the DR-device architecture supplemented with a deontic defeasible logic of violation. We motivate the choice for the logic and we show how to extend RuleML to capture the notions relevant to describe e-contracts for a monitoring perspective in Defeasible Logic. <s> BIB002
Defeasible deontic logic of violation as proposed by Governatori  and later refined by Governatori and Pham BIB002 extends defeasible logic BIB001 and adds deontic modalities. In its basic form, defeasible logic provides a method of reasoning about rules and precedence among those rules. Rules are similar to implications in that if we have Then if α is known to be true, β is also known to be true. However, contradictory facts can defeat previously known facts. For example if we have And r 2 > r 1 , then r 2 has precedence over r 1 and therefore we know that ¬β must be true. The extension proposed by Governatori and Pham takes defeasible logic and introduces deontic predicates.