Scope and conventions

The motivating proposal refers to an Enter calculus, an ECB confluence result, and a companion manuscript entitled From the Enter Calculus to Relativistic Causal Structure. Their complete syntax, residual theory, and proof texts are not premises of this paper. Consequently:

1. the operational model below is self-contained;

2. no result is attributed to an unspecified Enter type system;

3. any application to a particular calculus must verify the stated hypotheses;

4. geometric representation assumptions are not presented as consequences of confluence.

We use $\mathbb{N}=\{0,1,2,\dots \}$. All vector spaces are finite-dimensional and real unless stated otherwise. A proper cone is a closed, convex, pointed cone with nonempty interior in its ambient space. Here pointed means $K\cap (-K)=\{0\}$. The notation $\mathrm{cone}A$ denotes all finite nonnegative linear combinations of elements of $A$.