The model of Iris lives in the category of \emph{Complete Ordered Families of Equivalences} (COFEs).
This definition varies slightly from the original one in~\cite{catlogic}.
This definition varies slightly from the original one in~\cite{catlogic}.
\begin{defn}[Chain]
\begin{defn}[Chain]
Given some set $\cofe$ and an indexed family $({\nequiv{n}}\subseteq\cofe\times\cofe)_{n \in\mathbb{N}}$ of equivalence relations, a \emph{chain} is a function $c : \mathbb{N}\to\cofe$ such that $\All n, m. n \leq m \Ra c (m)\nequiv{n} c (n)$.
Given some set $\cofe$ and an indexed family $({\nequiv{n}}\subseteq\cofe\times\cofe)_{n \in\mathbb{N}}$ of equivalence relations, a \emph{chain} is a function $c : \mathbb{N}\to\cofe$ such that $\All n, m. n \leq m \Ra c (m)\nequiv{n} c (n)$.