From 404749206c0e83e8bed5f866245b432268c876d9 Mon Sep 17 00:00:00 2001
From: Ralf Jung
Date: Sun, 10 Dec 2017 14:11:16 +0100
Subject: [PATCH] docs: banach: make f^k part of the theorem, nut just a
remark; extend ref to americarutten

docs/algebra.tex  3 +
docs/programlogic.tex  2 +
2 files changed, 2 insertions(+), 3 deletions()
diff git a/docs/algebra.tex b/docs/algebra.tex
index dc5dfad2..dc8bdead 100644
 a/docs/algebra.tex
+++ b/docs/algebra.tex
@@ 90,10 +90,9 @@ Completeness is necessary to take fixedpoints.
\begin{thm}[Banach's fixedpoint]
\label{thm:banach}
Given an inhabited COFE $\ofe$ and a contractive function $f : \ofe \to \ofe$, there exists a unique fixedpoint $\fixp_T f$ such that $f(\fixp_T f) = \fixp_T f$.
+Moreover, this theorem also holds if $f$ is just nonexpansive, and $f^k$ is contractive for an arbitrary $k$.
\end{thm}
The above theorem also holds if $f^k$ is contractive for an arbitrary $k$.

\begin{thm}[America and Rutten~\cite{AmericaRutten:JCSS89,birkedal:metricspace}]
\label{thm:america_rutten}
Let $1$ be the discrete COFE on the unit type: $1 \eqdef \Delta \{ () \}$.
diff git a/docs/programlogic.tex b/docs/programlogic.tex
index de5055c1..7e7f2e00 100644
 a/docs/programlogic.tex
+++ b/docs/programlogic.tex
@@ 36,7 +36,7 @@ Furthermore, since the $\iFunc_i$ are locally contractive, so is $\textdom{ResF}
Now we can write down the recursive domain equation:
\[ \iPreProp \cong \UPred(\textdom{ResF}(\iPreProp, \iPreProp)) \]
Here, $\iPreProp$ is a COFE defined as the fixedpoint of a locally contractive bifunctor, which exists by \thmref{thm:america_rutten}.
+Here, $\iPreProp$ is a COFE defined as the fixedpoint of a locally contractive bifunctor, which exists and is unique up to isomorphism by \thmref{thm:america_rutten}.
We do not need to consider how the object $\iPreProp$ is constructed, we only need the isomorphism, given by:
\begin{align*}
\Res &\eqdef \textdom{ResF}(\iPreProp, \iPreProp) \\

2.26.2