Guaranteeing the correctness of critical and complex software and systems is a challenge that needs to be tackled right from the requirements engineering phase. This paper introduces two development patterns linked to the shape of requirements. The first one allows to automatically formalize a constraint and introduce it in an existing system. The second one is interested on requirements describing a sequence of operations. The verification activity is partly automated and the validation becomes easier to manage. The approach using these development patterns allow us an incremental development of formal specifications and their associated requirements, linked by a glossary. The case study of a hemodialysis system is used as a running example throughout this paper.