Structural operational semantic specifications come in different styles: small-step and big-step. A problem with the big-step style is that specifying divergence and abrupt termination gives rise to annoying duplication. We present a novel approach to representing divergence and abrupt termination in big-step semantics using status flags. This avoids the duplication problem, and uses fewer rules and premises for representing divergence than previous approaches in the literature.
 Big-step semantics for languages with abrupt termination and or divergence suffer from a serious duplication problem, addressed by the novel 'pretty-big-step' style presented by Chargueraud at ESOP'13. Such rules are less concise than corresponding small-step rules, but they have the same advantages as big-step rules for program correctness proofs. Here, we show how to automatically derive pretty-big-step rules directly from small-step rules by 'refocusing'. This gives the best of both worlds: we only need to write the relatively concise small-step specifications, but our reasoning can be big-step as well as small-step. The use of strictness annotations to derive small-step congruence rules gives further conciseness. Dealing with polymorphism in the presence of imperative features is a long-standing open problem for Hindley-Milner type systems. A widely adopted approach is the value restriction, which inhibits polymorphic generalisation and unfairly rejects various programs that cannot go wrong. We consider abstract interpretation as a tool for constructing safe and precise type systems, and investigate how to derive store-based types by abstract interpretation. We propose store-based types as a type discipline that holds potential for interesting and flexible alternatives to the value restriction.