This paper develops a closure-based framework for understanding mathematical structure. Instead of treating mathematical objects as primitive entities defined solely by axioms, the framework proposes that admissible mathematical structure is characterized by stability under three canonical operations: presentation collapse, inferential persistence, and canonical completion. Within this approach, mathematical lawhood is defined by a fixed-point closure condition. A candidate structure is admissible if it remains invariant under these three operators. Presentation collapse removes representational scaffolding and identifies equivalent formulations. Inferential persistence retains structure that survives admissible transformations such as proof, re-expression, and weakening of assumptions. Canonical completion selects the canonical representative of the resulting admissible class. The paper establishes two central structural results. First, the operator triple governing this closure process is shown to be inevitable: any admissibility diagnostic satisfying minimal structural conditions reduces to the same three-stage form. Second, the resulting closure recursion possesses a unique fixed point under a finite set of structural assumptions based on Noetherian descent and admissibility stability. This perspective interprets familiar mathematical structures such as groups, topological spaces, and categories as closure-stable fixed points rather than primitive axiomatic objects. The framework therefore provides a structural criterion for distinguishing essential mathematical content from representational scaffolding. The work forms the mathematical sector of a broader closure-based framework that also applies to physical law. However, the present paper focuses entirely on the mathematical formulation of closure-stable structure and the fixed-point admissibility principle that defines it.