Mix $\star$-autonomous quantales and the continuous weak order

Abstract

The set of permutations on a finite set can be given a lattice structure (known as the weak Bruhat order). The lattice structure is generalized to the set of words on a fixed alphabet $\Sigma = \{ x, y, z, ... \}$, where each letter has a fixed number of occurrences (these lattices are known as multinomial lattices and, in dimension 2, as lattices of lattice paths). By interpreting the letters $x, y, z, ...$ as axes, these words can be interpreted as discrete increasing paths on a grid of a $d$-dimensional cube, where $d = {\rm card}(\Sigma)$. We show in this paper how to extend this order to images of continuous monotone paths from the unit interval to a $d$-dimensional cube. The key tool used to realize this construction is the quantale $\mathsf{L}_{\vee}(\mathbb{I})$ of join-continuous functions from the unit interval to itself; the construction relies on a few algebraic properties of this quantale: it is $\star$-autonomous and it satisfies the mix rule. We begin developing a structural theory of these lattices by characterizing join-irreducible elements, and by proving these lattices are generated from their join-irreducible elements under infinite joins.