1 \documentclass[12pt]{article}
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2 \usepackage{blindtext}
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3 \usepackage{enumerate}
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4 \usepackage{hyperref, bookmark}
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5 \usepackage{amsmath, amsfonts, amssymb, amsthm}
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8 \title{Strong Separation}
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10 \date{\vspace{-2em}\today{}}
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13 \renewcommand{\Lam}[2]{\lambda#1.\, \{\!\!\{#2\}\!\!\}}
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19 \section*{The Calculus}
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20 \subparagraph{Syntax}
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21 \[\begin{array}{lll}
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22 \tm, \tmtwo & \ddef & \var \mid \tm\,\tmtwo \mid \Lam\var{\tm\Comma\vec\tm} \\
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23 n & \ddef & \Lam\var{n\Comma\vec n} \mid \var\,\vec n \\
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25 C & \ddef & \Box \mid C\,\tm \mid \tm\,C \\
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26 P & \ddef & \vec\tm \Comma \Box \Comma \vec\tm \mid \vec\tm \Comma C[\Lam\var P] \Comma \vec\tm \\
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29 \subparagraph{Reduction rules}
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30 \[\begin{array}{lll}
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31 P[C[(\Lam\var{\tm\Comma\vec\tm})\,\tmtwo]] & \Red{}{\var\in \tm,\vec\tm} &
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32 P[C[\tm\Subst\var\tmtwo]\Comma \vec\tm\Subst\var\tmtwo]\\
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33 P[C[(\Lam\var{\tm\Comma\vec\tm})\,\tmtwo]] & \Red{}{\var\not\in\tm,\vec\tm} &
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34 P[C[\tm] \Comma \vec\tm\Comma\tmtwo]\\
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37 \subparagraph{Properties}
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39 \item Every term is normalizing iff it is strongly normalizing.
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40 \item Ogni strategia e' perpetua!
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45 \section*{Separation}
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46 \newcommand{\HeadOf}[1]{\operatorname{head}(#1)}
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47 \newcommand{\FstOf}[1]{\operatorname{fst}(#1)}
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48 \newcommand{\DegOf}[1]{\operatorname{deg}(#1)}
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49 \newcommand{\SubtmOf}[2]{#1\preceq #2}
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51 % \item \textbf{$\boldsymbol\sigma$-separation.}
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52 % \textcolor{red}{come definirlo? con le variabili? con i termini?
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53 % problematico in cbv}
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54 % Two terms are $\sigma$-separable iff there exists a substitution
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55 % $\sigma$ such that \textcolor{red}{???}
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56 % \item \textbf{Semi-$\boldsymbol\sigma$-separation.}
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57 % Two terms are semi-$\sigma$-separable iff there exists a substitution
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58 % $\sigma$ such that -- in short -- it makes one diverge and the other one converge.
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59 % \item \textbf{Our subproblem:} Semi-$\sigma$-separating two (usual) $\boldsymbol\lambda$-terms
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60 % (in deep normal form)
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61 \item \textbf{Subterm:} $\SubtmOf\tm\tmtwo$ means that $\tm$ is an ($\eta/\Omega$)-subterm of $\tmtwo$.
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62 \item \textbf{Distinction:} Let $T_x \defeq \{t \preceq T \mid \HeadOf{t} = \HeadOf{D} \}$.
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63 Now: $C_x$ is $D$--\emph{distinct} iff it is empty, or there exists path $\pi$ s.t.:
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65 \item \emph{effective} for $D$, cioe' $\FstOf{\pi} \leq \DegOf{D}$;
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66 \item $\forall t\in D_x$, $t_\pi \neq \Omega$;
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67 \item $\exists t\in C_x$ s.t. $t \not\sim_\pi D$;
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68 \item $\{t\in C_x \mid t \sim_\pi D\}$ is $D$--distinct.
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