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update blueprint dependencies
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Antoine-dSG committed Aug 13, 2024
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2 changes: 1 addition & 1 deletion README.md
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In this project, we formalise in Lean 4 the claim that the sequence of maximums of values of (Coxeter) frieze patterns is the Fibonacci sequence.
A Latex file with the exact statements will be made available i) on the blueprint, and ii) in the note "On upper bounds in frieze patterns" posted at https://arxiv.org/pdf/2407.16717 .
A Latex file with the exact statements is available i) on the blueprint (here: https://antoine-dsg.github.io/frieze_patterns/blueprint/), and ii) in the note "On upper bounds in frieze patterns" (here: https://arxiv.org/pdf/2407.16717).

Most of the project will consist in formalising the pre-requisits, including:
1) Definition of a (Coxeter) frieze pattern
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23 changes: 14 additions & 9 deletions blueprint/src/chapter2.tex
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Expand Up @@ -10,7 +10,7 @@ \chapter{Sequence of maxima of frieze patterns}

This leads to the following two definitions.
\begin{definition}
\label{def:un(f)}
\label{def:unf}
\uses{cor:imageFinite}
For each $n \in \mathbb{N}^*$ and each $f \in {\rm Frieze}(n)$, there is a well-defined positive integer
\[
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\begin{definition}
\label{def:un}
\uses{def:un(f),prop:friezeFinite}
\uses{def:unf,prop:friezeFinite,l:friezeNonEmpty}
For each $n$, there is a well-defined
positive integer, called the {\it maximum value} among arithmetic frieze patterns of height $n$, which we write as
\[
u_n := \max (u_n(f) : f \in {\rm Frieze}(n)).
\]
\end{definition}

\begin{definition}
\label{def:fib}
The Fibonacci sequence $(F_n)_{n \in \mathbb{N}}$ is defined by $F_0 = 0, F_1 = 1$ and the recursive formula
\[
F_n = F_{n-1} + F_{n-2}.
\]
\end{definition}


We are now able to formulate and prove the main theorem of this section.
\begin{theorem}
\label{MainTheorem}
\uses{def:un, l:unLB, l:unUB}
For all $n \geq 1$, we have
\[
u_n = F_{n},
\]
where $(F_{n})_{n \in \mathbb{N}}$ is the {\it Fibonacci sequence}, i.e. the sequence recursively defined by
$F_0 = 0, F_1 = 1$ and the recursive formula
\[
F_n = F_{n-1} + F_{n-2}.
\]
u_n = F_{n}.
\]
\end{theorem}
We break down the proof into two lemmas.

\begin{lemma}
\label{l:unLB}
\uses{def:un,l:testCriteria, def:fib}
For all $n \geq 1$, we have
\[
u_n \geq F_{n}.
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We now turn to the reverse equality.
\begin{proposition}
\label{l:unUB}
\uses{def:un,l:testCriteria, def:fib}
For all $n \geq 1$, we have
\[
u_n \leq F_{n}.
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