"Presidential Decree No. XXX, which implemented (or "implements," depending on context) Law No. ZZZ..." In many (if not most) Spanish-speaking countries, the enactment of legislation involves two steps: first, the drafting and approval (by the National Assembly or equivalent) of the law, and then the issuance of a decree (usually signed by the chief executive authority, e.g., the president of the country) that implements the approved legislation. The legislation is unenforceable until the decree has been issued. -- HTH, HC