\newcommand{\sem}[1]{[\![ #1 ]\!]}
\newcommand{\R}{\,\mathscr{R}\,}
+\newcommand{\N}{\,\mathbb{N}\,}
+\newcommand{\NT}{\,\mathbb{N}\,}
+\newcommand{\NH}{\,\mathbb{N}\,}
\title{...}
\author{...}
\item $plus\_O:\forall x.x+0=x$
\item $plus\_S:\forall x,y.x+S(y)=S(x+y)$
\item $times\_O:\forall x.x*0=0$
-\item $timies\_S:\forall x,y.x*S(y)=x+(x*y)$
+\item $times\_S:\forall x,y.x*S(y)=x+(x*y)$
\end{itemize}
\noindent
\[
(\forall_i)\frac{\Gamma \vdash M:P}{\Gamma \vdash
- \lambda x:N.M: \forall x.P}(*) \hspace{2cm}
+ \lambda x:\N.M: \forall x.P}(*) \hspace{2cm}
(\forall_e)\frac{\Gamma \vdash M :\forall x.P}{\Gamma \vdash M t: P[t/x]}
\]
\item $\sem{A} = 1$ if A is atomic
\item $\sem{A \land B} = \sem{A}\times \sem{B}$
\item $\sem{A \to B} = \sem{A}\to \sem{B}$
-\item $\sem{\forall x.P} = N \to \sem{P}$
-\item $\sem{\exists x.P} = N \times \sem{P}$
+\item $\sem{\forall x.P} = \N \to \sem{P}$
+\item $\sem{\exists x.P} = \N \times \sem{P}$
\end{itemize}
definition.
\begin{itemize}
\item $\sem{nat\_ind} = R$
-\item $\sem{ex\_ind} = (\lambda f:(N \to \sem{P} \to \sem{Q}).
-\lambda p:N\times \sem{P}.f (fst \,p) (snd \,p)$.
-\item $\sem{ex\_intro} = \lambda x:N.\lambda f:\sem{P}.<x,f>$
+\item $\sem{ex\_ind} = (\lambda f:(\N \to \sem{P} \to \sem{Q}).
+\lambda p:\N\times \sem{P}.f (fst \,p) (snd \,p)$.
+\item $\sem{ex\_intro} = \lambda x:\N.\lambda f:\sem{P}.<x,f>$
\item $\sem{fst} = fst$
\item $\sem{snd} = snd$
\item $\sem{conj} = \lambda x:\sem{P}.\lambda y:\sem{Q}.<x,y>$
\item $\sem{false\_ind} = \bot_{\sem{Q}}$
-\item $\sem{discriminate} = \lambda \_:N.\lambda \_:1.*$
-\item $\sem{injS}= \lambda \_:N. \lambda \_:N.\lambda \_:1.*$
-\item $\sem{plus\_O} = \sem{times\_O} = \lambda \_:N.*$
-\item $\sem{plus\_S} = \sem{times_S} = \lambda \_:N. \lambda \_:N.*$
+\item $\sem{discriminate} = \lambda \_:\N.\lambda \_:1.*$
+\item $\sem{injS}= \lambda \_:\N. \lambda \_:\N.\lambda \_:1.*$
+\item $\sem{plus\_O} = \sem{times\_O} = \lambda \_:\N.*$
+\item $\sem{plus\_S} = \sem{times_S} = \lambda \_:\N. \lambda \_:\N.*$
\end{itemize}
In the case of structured proofs:
\begin{itemize}
\item $\sem{M N} = \sem{M} \sem{N}$
\item $\sem{\lambda x:A.M} = \lambda x:\sem{A}.\sem{M}$
-\item $\sem{\lambda x:N.M} = \lambda x:N.\sem{M}$
+\item $\sem{\lambda x:\N.M} = \lambda x:\N.\sem{M}$
\item $\sem{M t} = \sem{M} \sem{t}$
\end{itemize}
\end{itemize}
\noindent
-We proceed to prove that alla axioms $ax:Ax$ are realized by $\sem{ax}$.
+We proceed to prove that all axioms $ax:Ax$ are realized by $\sem{ax}$.
\begin{itemize}
\item $nat\_ind$. We must prove that the recursion schema $R$ realizes the