BitML is a process calculus to express smart contracts that can be run on Bitcoin. One of its current limitations is that, once a contract has been stipulated, the participants cannot renegotiate its terms: this prevents expressing common financial contracts, where funds have to be added by participants at run-time. In this paper, we extend BitML with a new primitive for contract renegotiation. At the same time, the new primitive can be used to write recursive contracts, which was not possible in the original BitML. We show that, despite the increased expressiveness, it is still possible to execute BitML on standard Bitcoin, preserving the security guarantees of BitML.

中文翻译：

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比特币合约中的重新协商和递归

BitML 是一种过程演算，用于表达可以在比特币上运行的智能合约。它目前的局限性之一是，一旦约定了合同，参与者就无法重新谈判其条款：这阻止了表达共同的金融合同，参与者必须在运行时添加资金。在本文中，我们使用新的合约重新协商原语扩展了 BitML。同时，新的原语可用于编写递归合约，这在原始 BitML 中是不可能的。我们表明，尽管表达能力有所提高，但仍然可以在标准比特币上执行 BitML，同时保留了 BitML 的安全保证。