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BelegCuthalion committed May 31, 2020
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6 changes: 3 additions & 3 deletions cut-elimination.tex
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\section{Lemma}\label{true-assum} If $~\small\text{GSTL}^- + \nabla Cut \vdash \mathcal{S} , \p^r \top^n \Rightarrow \Delta$ then $\small\text{GSTL}^- + \nabla Cut \vdash \mathcal{S} \Rightarrow \Delta$ with a proof of at most the same rank.

\textit{Proof:} Suppose $\mathbf{D}$ is a proof tree for $\mathcal{S} , \p^r \top^n \Rightarrow \Delta$. By induction on $h(\mathbf{D})$, induction hypothesis states that for any proof tree $\mathbf{D}'$ with conclusion $\mathcal{S'} , \p^{r'} \top^{n'} \Rightarrow \Delta'$ such that $h(\mathbf{D}') < h(\mathbf{D})$, there is a proof $\mathbf{D}''$ of $\mathcal{S}' \Rightarrow \Delta'$ such that $\rho(\mathbf{D}'') \leq \rho(\mathbf{D}')$.
\textit{Proof}: Suppose $\mathbf{D}$ is a proof tree for $\mathcal{S} , \p^r \top^n \Rightarrow \Delta$. By induction on $h(\mathbf{D})$, induction hypothesis states that for any proof tree $\mathbf{D}'$ with conclusion $\mathcal{S'} , \p^{r'} \top^{n'} \Rightarrow \Delta'$ such that $h(\mathbf{D}') < h(\mathbf{D})$, there is a proof $\mathbf{D}''$ of $\mathcal{S}' \Rightarrow \Delta'$ such that $\rho(\mathbf{D}'') \leq \rho(\mathbf{D}')$.

Consider different cases for the last rule of $\mathbf{D}$, with possible sub-trees $\mathbf{D_0}$ and $\mathbf{D_1}$. $Ta$ and $Ex$ cases are trivially ruled out. In $Id$ case (which implies $n = 1$ and $r = 0$), we have $\Rightarrow \top$ by $Ta$. In $Lw$ case, where an instance of $\top$ is principal and $n = 1$, $\mathbf{D_0}$ itself proves the desired sequent. If $n > 1$, then the induction hypothesis with $n' = n - 1$ gives the desired sequent. $Lc$ on an instance of $\top$ is similar, with $n' = n + 1$. In all other cases, just apply induction hypothesis on $\mathbf{D_0}$ (and possibly $\mathbf{D_1}$), then the same last rule. Notice in all cases we must apply induction hypothesis with $n' = n$ and $r' = r$, except for $R\rightarrow$ and $R\nabla$, in which we apply it with $r' = r + 1$ and $r' = r - 1$ respectively. Also notice that $\nabla Cut$ is not used except in $\nabla Cut$ case, where it is applied with the same cut-formula, so the resulting proof tree is not of a higher rank than $\mathbf{D}$.

\section{Theorem}\label{cut-admis} \emph{Cut Reduction for GSTL: } For any $\mathcal{S}$, $n>0$, $A$, $\mathcal{T}$, $k$, $l$ and $\Delta$, if $~\small\text{GSTL}^- + \nabla Cut \vdash \mathcal{S} \Rightarrow \nabla^k A$ and $\small\text{GSTL}^- + \nabla Cut \vdash$ $\mathcal{T} , \p^{l+k} A^n \Rightarrow \Delta$ with proof trees of ranks less than $\rho(A)$, then
$\small\text{GSTL}^- + \nabla Cut \vdash \p^l \mathcal{S} , \mathcal{T}$ $\Rightarrow \Delta$ also with a proof tree of a rank less than $\rho(A)$.

\emph{Proof:}
\textit{Proof}:
Let $\mathbf{D_0}$ and $\mathbf{D_1}$ be proof trees of ranks less than $\rho(A)$, with conclusions $\mathcal{S} \Rightarrow \nabla^k A$ and $\mathcal{T} , \p^{l+k} A^n \Rightarrow \Delta$ and heights $h(\mathbf{D_0})$ and $h(\mathbf{D_1})$ respectively.
\begin{prooftree}
\noLine
Expand Down Expand Up @@ -120,7 +120,7 @@ \section{Theorem}\label{cut-admis} \emph{Cut Reduction for GSTL: } For any $\mat
\section{Corollary} \emph{$\nabla$Cut Elimination for GSTL: }
If $\small\text{GSTL}^- + \nabla Cut \vdash \Gamma \Rightarrow \Delta$, then $\small\text{GSTL}^- \vdash \Gamma \Rightarrow \Delta$.

\emph{Proof:} It suffices to show that for any proof tree of $\Gamma \Rightarrow \Delta$ like $\mathbf{D}$, there is another proof of it with a lower rank. Using induction on $h(\mathbf{D})$, the induction hypothesis states that for any proof of $\Gamma' \Rightarrow \Delta'$ like $\mathbf{D'}$ such that $h(\mathbf{D'}) < h(\mathbf{D})$, there is another proof of $\Gamma' \Rightarrow \Delta'$ like $\mathbf{D''}$ such that $\rho(\mathbf{D''}) < \rho(\mathbf{D'})$. Particularly for the immediate sub-trees of $\mathbf{D}$, this gives us sub-trees with lower cut-rank, which we call $\mathbf{D}_i$. We now consider two cases for the last rule of $\mathbf{D}$
\textit{Proof}: It suffices to show that for any proof tree of $\Gamma \Rightarrow \Delta$ like $\mathbf{D}$, there is another proof of it with a lower rank. Using induction on $h(\mathbf{D})$, the induction hypothesis states that for any proof of $\Gamma' \Rightarrow \Delta'$ like $\mathbf{D'}$ such that $h(\mathbf{D'}) < h(\mathbf{D})$, there is another proof of $\Gamma' \Rightarrow \Delta'$ like $\mathbf{D''}$ such that $\rho(\mathbf{D''}) < \rho(\mathbf{D'})$. Particularly for the immediate sub-trees of $\mathbf{D}$, this gives us sub-trees with lower cut-rank, which we call $\mathbf{D}_i$. We now consider two cases for the last rule of $\mathbf{D}$

\begin{enumerate}[label=\Roman*]
\item If the last rule of $\mathbf{D}$ is of a lower rank than $\rho(\mathbf{D})$, i.e. the $\nabla Cut$ rule with the maximum rank is not the last rule in $\mathbf{D}$, then we can apply the same last rule on $\mathbf{D}_i$s and get a proof of $\Gamma \Rightarrow \Delta$ with a lower rank.
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61 changes: 56 additions & 5 deletions iSTL.tex
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Expand Up @@ -42,13 +42,13 @@ \section{iSTL$^-$} An iSTL sequent $\Gamma \Rightarrow \Delta$ is a binary relat
\\
\begin{multicols}{3}
\begin{prooftree}
\RightLabel{$L\land$}
\RightLabel{$L\land_1$}
\AXC{$\Gamma , A \Rightarrow \Delta$}
\UIC{$\Gamma , A \land B \Rightarrow \Delta$}
\end{prooftree}
\columnbreak
\begin{prooftree}
\RightLabel{$L\land$}
\RightLabel{$L\land_2$}
\AXC{$\Gamma , B \Rightarrow \Delta$}
\UIC{$\Gamma , A \land B \Rightarrow \Delta$}
\end{prooftree}
Expand All @@ -70,13 +70,13 @@ \section{iSTL$^-$} An iSTL sequent $\Gamma \Rightarrow \Delta$ is a binary relat
\end{prooftree}
\columnbreak
\begin{prooftree}
\RightLabel{$R\lor$}
\RightLabel{$R\lor_1$}
\AXC{$\Gamma \Rightarrow A$}
\UIC{$\Gamma \Rightarrow A \lor B$}
\end{prooftree}
\columnbreak
\begin{prooftree}
\RightLabel{$R\lor$}
\RightLabel{$R\lor_2$}
\AXC{$\Gamma \Rightarrow B$}
\UIC{$\Gamma \Rightarrow A \lor B$}
\end{prooftree}
Expand Down Expand Up @@ -111,4 +111,55 @@ \subsection{Cut}
\BIC{$\Gamma , \Gamma' \Rightarrow \Delta$}
\end{prooftree}
By $\text{iSTL}$ we mean $\text{iSTLL}^- + Cut$
\pagebreak

\subsection{Lemma} iSTL proves

\subsubsection{}\label{lem:i-nabla-dist-and} $\nabla^n (A \land B) \Rightarrow \nabla^n A \land \nabla^n B$

\textit{Proof}:
\begin{prooftree}
\AXC{}
\RightLabel{$Id$}
\UIC{$A \Rightarrow A$}
\RightLabel{$L\land_1$}
\UIC{$A \land B \Rightarrow A$}
\RightLabel{$N$} \doubleLine
\UIC{$\nabla^n (A \land B) \Rightarrow \nabla^n A$}

\AXC{}
\RightLabel{$Id$}
\UIC{$B \Rightarrow B$}
\RightLabel{$L\land_2$}
\UIC{$A \land B \Rightarrow B$}
\RightLabel{$N$} \doubleLine
\UIC{$\nabla^n (A \land B) \Rightarrow \nabla^n B$}

\RightLabel{$R\land$}
\BIC{$\nabla^n (A \land B) \Rightarrow \nabla^n A \land \nabla^n B$}
\end{prooftree}

\subsubsection{}\label{lem:i-nabla-dist-or} $\nabla^n (A \lor B) \Rightarrow \nabla^n A \lor \nabla^n B$ \todo{}

\subsubsection{}\label{lem:i-nabla-dist-imp} $\nabla^n (A \rightarrow B) \Rightarrow \nabla^n A \rightarrow \nabla^n B$

\textit{Proof}:
\begin{prooftree}
\AXC{}
\RightLabel{$Id$}
\UIC{$A \Rightarrow A$}

\AXC{}
\RightLabel{$Id$}
\UIC{$B \Rightarrow B$}
\RightLabel{$Lw$}
\UIC{$A , B \Rightarrow B$}

\RightLabel{$L\rightarrow$}
\BIC{$\nabla (A \rightarrow B) , A \Rightarrow B$}
\RightLabel{$N$} \doubleLine
\UIC{$\nabla^{n+1} (A \rightarrow B) , \nabla^n A \Rightarrow \nabla^n B$}
\RightLabel{$R\rightarrow$}
\UIC{$\nabla^n (A \rightarrow B) \Rightarrow \nabla^n A \rightarrow \nabla^n B$}
\end{prooftree}

\subsubsection{}\label{lem:i-nabla-fact-imp} $\nabla^n A \rightarrow \nabla^n B \Rightarrow \nabla^n (A \rightarrow B)$ \todo{is this even possible?}
1 change: 1 addition & 0 deletions preamble.tex
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Expand Up @@ -29,4 +29,5 @@
\newcommand{\caseref}[1]{\hyperref[#1]{\ref{#1}}}
\newcommand{\rot}{\rotatebox{90}}
\newcommand{\p}{\partial}
\newcommand{\todo}[1]{{\color{red}\textbf{TODO} #1}}
\EnableBpAbbreviations
1 change: 0 additions & 1 deletion table-cut-reduction-cases.tex
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Expand Up @@ -60,5 +60,4 @@
\multicolumn{2}{|c|}{\slashbox[2.3cm]{$\mathbf{D_0}$}{$\mathbf{D_1}$}} & \rot{$Id$} & \rot{$Ta$} & \rot{$Ex$} & \rot{$Lw$} & \rot{$Lc$} & \rot{$\nabla Cut$} & \rot{$L \land_1$} & \rot{$L \land_2$} & \rot{$L \lor$} & \rot{$L \nabla$} & \rot{$L \rightarrow$} & \rot{$Rw$} & \rot{$R \land$} & \rot{$R \lor_1$} & \rot{$R \lor_2$} & \rot{$R \rightarrow$} & \rot{$R \nabla$} \\
\hline
\end{tabular}
\caption{sadf}
\end{table}

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