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\chapter{Class 1} |
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\chapter{Class 2} | ||
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\begin{tabular}{l|l|c} | ||
Goal & Knowledge & Outermost symbol \\ | ||
\hline | ||
\pbox{20cm}{Show for all $x$, $G(x)$. \\ Consider arbitrary $\hat{x}$.\\ Show $G(\hat{x})$} & \pbox{20cm}{We know for all $x$, $K(x)$ \\ In particular we know $K(\hat{t})$ for constant $\hat{t}$} & $\forall$ \\ | ||
\hline | ||
\pbox{20cm}{Show: exists $x$ s.t. $G(x)$. \\ We show $G(\hat{t})$} & \pbox{20cm}{We know exists $x$ s.t. $K(x)$ \\ Let $\hat{x}$ be s.t. $K(x)$} & $\exists$ \\ | ||
\hline | ||
\pbox{20cm}{Show $G_1$ iff $G_2$ \\ 1. Show if $G_1$ then $G_2$\\ 2. Show if $G_2$ then $G_1$} & \pbox{20cm}{We know $K_1$ iff $K_2$\\ In particular we know if $K_1$ then $K_2$\\ and if $K_2$ then $K_1$} & $\iff$ \\ | ||
\hline | ||
\pbox{20cm}{Show if $G_1$ then $G_2$ \\ Assume $G_1$\\ Show $G_2$} & \pbox{20cm}{We know if $K_1$ then $K_2$\\ 1. To show $K_2$ it suffices to show $K_2$\\ 2. Know $K_1$, Also know $K_2$} & $\Rightarrow$ \\ | ||
\hline | ||
\pbox{20cm}{Show $G_1$ and $G_2$\\ 1. Show $G_1$\\ 2. Show $G_2$} & \pbox{20cm}{Know $K_1$ and $K_2$\\ 1. Also Know $K_1$ \\ 2. Also Know $K_2$} & $\wedge$ \\ | ||
\hline | ||
\pbox{20cm}{Show $G_1$ or $G_2$\\ 1. Assume $\neg G_1$, show $G_2$\\ 2. Assume $\neg G_2$, show $G_1$} & \pbox{20cm}{We know $K_1$ or $K_2$. Show $G$.\\ | ||
1. Assume $K_1$, Show $G$\\ 2. Assume $K_2$, Show $G$ \\ Case split $\uparrow$} & $\vee$ \\ | ||
\hline | ||
\multicolumn{2}{c|}{\pbox{20cm}{Move Negation Inside, as far as possible}} & $\neg$ \\ | ||
\hline | ||
\end{tabular} | ||
\section{Lattices and Fixpoints} | ||
We begin by defining relations and their properties. | ||
\begin{definition} | ||
A binary \textbf{relation} $R$ on a set $A$ is a subset $R \subset A\times A$. \\ | ||
The relation $R$ is \textbf{reflexive} if for all $x$ in $A$, we have $R(x,x)$.\\ | ||
The relation $R$ is \textbf{Antisymmetric} if for all $x$ and $y$ in $A$, if $R(x,y)$ and $R(y,x)$ then $x=y$. \\ | ||
The relation $R$ is \textbf{transitive} if for all $x,y$ and $z$ in $A$, if $R(x,y)$ and $R(y,z)$ then $R(x,z)$.\\ | ||
The relation $R$ is a \textbf{partial order} if $R$ is reflexive, antisymmetric and transitive. \\ | ||
A \textbf{Poset} $(A,\sqsubseteq)$ is a set $A$ and a partial order $\sqsubseteq$ on $A$. | ||
\end{definition} | ||
\begin{example} | ||
The pair $(\N,\leq)$ where $\N$ is the set of natural numbers, is a poset.\\ | ||
For every set $B$, we have $(\P(B),\subseteq)$ where $\P(B)$ is the powerset of $B$, is a poset. | ||
\begin{figure}[h] | ||
\centering | ||
\includegraphics[width=0.7\linewidth]{images/poset.png} | ||
\end{figure} | ||
\end{example} | ||
\begin{definition} | ||
\begin{itemize} | ||
\item Let $(A,\sqsubseteq)$ be a poset. A function $F$ from $A$ to $A$ is \textbf{monotone} (order-preserving, homomorphism) if for all $x$ and $y$ in $A$, if $x \sqsubseteq y$, then $F(x) \sqsubseteq F(y)$. | ||
% | ||
\item $F$ has a fixpoint $x$ in $A$ if there exists $x$ in $A$ such that $F(x)=x$. | ||
\item $x$ in $A$ is a pre-fixpoint of $F$ if $x \sqsubseteq F(x)$ and is a post-fixpoint of $F$, if $F(x) \sqsubseteq x$. | ||
\end{itemize} | ||
\end{definition} | ||
\begin{definition} | ||
Let $(A,\sqsubseteq)$ be a poset. | ||
\begin{itemize} | ||
\item $x$ in $A$ is an \textbf{upper bound}(lower bound) on a subset $B$ of $A$ if for all $y$ in $B$, it holds that $y \sqsubseteq x$ ($x \sqsubseteq y$). | ||
\item $x$ is the least upper bound of $B$ if (i) $x$ is an upper bound of $B$ and (ii) for all upper bounds $y$ of $B$, we have $x \sqsubseteq y$. We denote such $x$ by $\bigsqcup B$. | ||
\item $x$ is the greatest lower bound of $B$ if (i) $x$ is a lower bound of $B$ and (ii) for all lower bounds $y$ of $B$, we have $y \sqsubseteq x$. We denote such $x$ by $\bigsqcap B$. | ||
\end{itemize} | ||
\end{definition} | ||
\begin{example} | ||
\begin{itemize} | ||
\item Consider the poset $(\N,\leq)$. Then for any $B \subseteq \N$, if $B$ is finite, $\bigsqcup B$ is well-defined and equal to $\max B$. If $B$ is infinite, then $\bigsqcup B$ does not exist. | ||
\item Consider the poset $(\N \cup \{\infty\},\leq)$ where for all $x$ in $\N$, it holds that $x \leq \infty$. Then for all $B \subseteq \N$, the least upper bound $\bigsqcup B$ is well-define. | ||
\item Let $A$ be any set and consider the poset $(\P(A),\subseteq)$. For any subset $B$ of $\P(A)$, it holds that $\bigsqcup B = \bigcup B$ and $\bigsqcap B = \bigcap B$. | ||
\end{itemize} | ||
\end{example} | ||
\begin{definition} | ||
Poset $(A,\sqsubseteq)$ is a \textbf{complete-lattice} if for all $B \subseteq A$, both $\bigsqcap B$ and $\bigsqcup B$ exist. | ||
\end{definition} | ||
\begin{example} | ||
Let $(A,\sqsubseteq)$ be a complete-lattice. | ||
\begin{itemize} | ||
\item $\bigsqcup A = \top$ | ||
\item $\bigsqcap A = \bot$ | ||
\item $\bigsqcup \varnothing = \bot$ | ||
\item $\bigsqcap \varnothing = \top$ | ||
\end{itemize} | ||
\end{example} | ||
\begin{theorem}[Knaster-Tarski] | ||
For every complete lattice $(A,\sqsubseteq)$ and monotone function $F$ on $A$, it holds that | ||
\begin{enumerate} | ||
\item $\bigsqcup \{x\in A| x \sqsubseteq F(x)\}$ is the unique greatest fixpoint of $F$. | ||
\item $\bigsqcap \{x \in A| F(x) \sqsubseteq x\}$ is the unique least fixpoint of $F$. | ||
\end{enumerate} | ||
\end{theorem} | ||
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\textbf{Homework.} Prove the Knaster Tarski Theorem. |
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\chapter{Class 3} |
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\documentclass{book} | ||
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\input{preamble} | ||
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\begin{document} | ||
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\include{title} | ||
\input{class_1.tex} | ||
\input{class_2.tex} | ||
\input{class_3.tex} | ||
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\backmatter | ||
\addcontentsline{toc}{chapter}{Index} | ||
\printindex | ||
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\end{document} |
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\title{Formalisms Every Computer Scientist Should Know} | ||
\author{Students in the class} | ||
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\newcommand{\booklicense}{ | ||
This work is marked with CC0 1.0. | ||
To view a copy of this license, visit http://creativecommons.org/publicdomain/zero/1.0 | ||
} | ||
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% Author subtitle | ||
% For example, university or geographical location | ||
\newcommand{\authorsubtitle}{ISTA} | ||
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% PACKAGES | ||
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% this package allows large \fontsize | ||
\usepackage{fix-cm} | ||
% this is for graphics. e.g. rectangle on title page | ||
\usepackage{tikz} | ||
% Used by equations | ||
\usepackage{amsmath} | ||
\usepackage{amssymb,amsfonts,amsthm,mathptmx} | ||
% Paper dimensions | ||
\usepackage[a4paper, total={6in, 8in}]{geometry} | ||
% Inserting images | ||
\usepackage{graphicx} | ||
% Index creation | ||
\usepackage{makeidx} | ||
% Initialize an index so we can add entries with \index | ||
\makeindex | ||
% Others | ||
\usepackage{pbox} | ||
\usepackage{stmaryrd} | ||
% Links | ||
\usepackage{hyperref} | ||
% Convenient references | ||
\usepackage{cleveref} | ||
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% MACROS | ||
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\newtheorem{theorem}{Theorem} | ||
\newtheorem{definition}{Definition} | ||
\newtheorem{example}{Example} | ||
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\newcommand{\N}{\mathbb{N}} | ||
\newcommand{\R}{\mathbb{R}} | ||
\renewcommand{\P}{\mathcal{P}} |
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\frontmatter | ||
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\begin{titlepage} | ||
\begin{flushleft} | ||
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% Title | ||
\textbf{\fontfamily{qcs}\fontsize{48}{54}\selectfont Formalisms Every Computer Scientist Should Know\\} | ||
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% Draw a line 4pt high | ||
\par\noindent\rule{\textwidth}{4pt}\\ | ||
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\vspace{\fill} | ||
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% Author and Location | ||
\textbf{\large \bookauthor}\\[3.5pt] | ||
\textbf{\large \textit{\authorsubtitle}} | ||
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\vspace{\fill} | ||
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\end{flushleft} | ||
\begin{flushleft} | ||
\vspace{\fill} | ||
License: \booklicense | ||
\end{flushleft} | ||
\end{titlepage} | ||
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% Three-level Table of Contents | ||
\setcounter{tocdepth}{3} | ||
\tableofcontents | ||
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