Multi-argument specialization semilattices

TL;DR

The work develops a rigorous algebraic framework for multi-argument specialization semilattices, defined by $a \\sqsubseteq^n b_1, \\dots, b_n$ interpreted as $a \\subseteq K b_1 \\\cup \\dots \\\cup K b_n$ within a closure space. It establishes a complete axiom system for these structures and constructs a free principal regular extension that is universal for $K$-homomorphisms. The paper proves that every model embeds into a closure-space derived structure and provides a canonical embedding into a closure semilattice, thereby connecting algebraic and topological/closure-theoretic perspectives. This unifies subreducts of topological spaces and closure spaces under a single framework and yields a canonical representation via closure-space embeddings.

Abstract

If $X$ is a closure space with closure $K$, we consider the semilattice $(\mathcal P(X), \cup)$ endowed with further relations $ x \sqsubseteq y_1, y_2, \dots, y_n$ (a distinct $n+1$-ary relation for each $n \geq 1$), whose interpretation is $x \subseteq Ky_1 \cup Ky_2 \cup \dots \cup Ky_n $. We present axioms for such "multi-argument specialization semilattices" and show that this list of axioms is complete for substructures, namely, every model satisfying the axioms can be embedded into some structure originated by some closure space as in the previous sentence. We also provide a canonical embedding of a multi-argument specialization semilattice into (the reduct of) some closure semilattice.

Theorems & Definitions (16)

• Remark 2.1
• Definition 3.1
• Definition 3.2
• Proposition 3.3
• Remark 4.1
• Definition 4.2
• Remark 4.3
• Theorem 4.4
• Lemma 4.5
• proof