Later credits: resourceful reasoning for the later modality

In the past two decades, step-indexed logical relations and separation logics have both come to play a major role in semantics verification research. More recently, they been married together form of like VST, iCAP, Iris, which provide powerful tools for (among other things) building semantic models richly typed languages Rust. these logics, propositions are given using model, reasoning is reflected into logic through so-called “later” modality. On one hand, this modality provides an elegant, high-level account reasoning; on when used sufficiently sophisticated ways, it can become nuisance, turning perfectly natural proof strategies dead ends. work, we introduce later credits , new technique escaping later-modality quagmires. By leveraging second ancestor logics—separation logic—later turn “the right eliminate later” ownable resource, subject all traditional modular principles logic. We develop theory context present several challenging examples proofs patterns were previously not possible Iris but now due credits.