% % Where $\Pacman \equiv \lambda\_.\,\Pacman$.\r
%\r
% \end{example}\r
+\clearpage\r
+\section{Tentativi $\mathbf X$--separability (July, 15$^{\mathbf{th}}\div\infty$)}\r
+\newcommand{\perm}{\pi}\r
+\newcommand{\Perm}[2]{\pi[#1,#2]}\r
+\newcommand{\xK}{\kappa}\r
+\newcommand{\xN}{n}\r
+\newcommand{\LAM}[2]{\Lambda_{#2,#1}}\r
+\newcommand{\LAMNK}{\LAM\xN\xK}\r
+\newcommand{\Apply}[2]{(#1\mapsto#2)}\r
+\newcommand{\kn}{$(\kappa,n)$}\r
+\newcommand{\knnf}{\kn{}-nf}\r
+\newcommand{\Lams}[1]{\operatorname{lams}(#1)}\r
+\newcommand{\Args}[1]{\operatorname{args}(#1)}\r
+\newcommand{\Head}[1]{\operatorname{head}(#1)}\r
+\begin{definition}[$\Lams\cdot,\Args\cdot,\Head\cdot$]\r
+ \[\Lams{\lambda\vec\var.\,\vartwo\,\vec\tm} \defeq |\vec\var| \]\r
+ \[\Args{\lambda\vec\var.\,\vartwo\,\vec\tm} \defeq |\vec\tm| \]\r
+ \[\Head{\lambda\vec\var.\,\vartwo\,\vec\tm} \defeq \vartwo \]\r
+\end{definition}\r
+\r
+\begin{definition}[\kn{}-normal forms]\r
+ First recall that terms in normal form have the shape\r
+ $\lambda\vec\var.\,\vartwo\,\vec\tm$, where the terms $\vec\tm$ are in normal form too.\r
+ \r
+ We define inductively the set of \knnf s (for $\xK,\xN$ natural numbers):\r
+ $\lambda\vec\var.\,\vartwo\,\vec\tm$ is a \knnf{} iff \r
+ $|\vec\var|\leq\xK$, $|\vec\tm|\leq\xN$, and every term in $\vec\tm$ is a \knnf{}.\r
+\end{definition}\r
+\r
+\begin{definition}[Permutator $\Perm\cdot\cdot$]~\r
+ \[\Perm i j \defeq \lambda\vec\var\vartwo.\,\vartwo\, \vec\alpha\,\vec\var\,\vartwo\]\r
+ where $\vec\var$, $\vec\alpha$ and $\vartwo$ are fresh variables,\r
+ with $|\vec\var| = i$ and $|\vec\alpha| = j$.\r
+\end{definition}\r
+\r
+\begin{definition}{$\Apply\cdot\cdot$}\r
+ We denote by $\tmtwo\Apply\var\tm$ the normal form of $\tmtwo\Subst\var\tm$ in normal form --\r
+ if it has one.\r
+\end{definition}\r
+\r
+\begin{lemma}\r
+ Let $\tm$ a \knnf, and $\Head\tm=\var$.\r
+ If $A\leq \Args\tm$ and $B \geq \xK + A + 1$,\r
+ let $\tmtwo\defeq\tm\Apply\var{\Perm{A}{B}}$ in:\r
+ $\Lams\tm=\Lams\tmtwo$ and $\tmtwo\in\LAM ? ?$\r
+\end{lemma}\r
+\begin{proof}\r
+ By induction on the normal form structure of $\tm$.\r
+ Let $\tm=\lambda\vec\var.\,\vartwo\,\vec\tmtwo$:\r
+ \begin{itemize}\r
+ \item if $\vartwo=\var$, then\r
+ $\tm\Apply\var\perm = \lambda\var_1\ldots\var_{???}.\,\var\,\vec\tmthree$\r
+ \item if $\vartwo\neq\var$, then $\tm\Apply\var\perm = \lambda\vec\var.\,\vartwo\,\vec\tmthree$\r
+ where $\vec\tmthree\defeq \vec\tmtwo\Apply\var\perm$.\r
+ Conclude by inductive hypothesis.\r
+ \end{itemize}\r
+\end{proof}\r
+\begin{corollary}\r
+ Let $\tm \defeq \var\,f_1\cdots f_m$ a \knnf.\r
+ If $A\leq m$ and $B \geq A + \xK$,\r
+ then $\tm\Apply\var{\Perm{A}{B}}$ is an inert.\r
+\end{corollary}\r
+\r
+\begin{lemma}\r
+ For every $\tm,\tmtwo$ be \knnf{s},\r
+ every fresh variable $\var$,\r
+ $\perm\defeq\Perm{i}{i+k+1}$ permutator,\r
+ $\tm\EtaEq\tmtwo$ iff $\tm\Apply\var\perm\EtaEq\tmtwo\Apply\var\perm$.\r
+\end{lemma}\r
\r
\end{document}\r