diff --git a/Advanced/Nonstandard Analysis/main.tex b/Advanced/Nonstandard Analysis/main.tex index e9edcc7..bcdf52e 100755 --- a/Advanced/Nonstandard Analysis/main.tex +++ b/Advanced/Nonstandard Analysis/main.tex @@ -32,13 +32,18 @@ } +% This handout is pretty difficult. Make sure you can all solve all the problems yourself, +% and remember that each SECTION was a two-hour lesson with a smart class. +% From experience, the following holds: +% supremum is a better lesson than dual numbers, which is better than extensions. + + \begin{document} \maketitle - - \input{parts/1 extensions} - \input{parts/2 dual} - \input{parts/x supremum} + \input{parts/supremum} + \input{parts/dual} + \input{parts/extensions} \end{document} diff --git a/Advanced/Nonstandard Analysis/parts/2 dual.tex b/Advanced/Nonstandard Analysis/parts/dual.tex similarity index 86% rename from Advanced/Nonstandard Analysis/parts/2 dual.tex rename to Advanced/Nonstandard Analysis/parts/dual.tex index 020b21c..b7eb55a 100644 --- a/Advanced/Nonstandard Analysis/parts/2 dual.tex +++ b/Advanced/Nonstandard Analysis/parts/dual.tex @@ -21,8 +21,7 @@ In the problems below, let $\varepsilon$ a positive infinitesimal so that $\vare \note{Note that $\varepsilon \neq 0$.} \definition{} -The set of \textit{dual numbers} is a nonarchimedian extension of $\mathbb{R}$ \par -that consists of elements of the form $a + b\varepsilon$, where $a, b \in \mathbb{R}$. +The set of \textit{dual numbers} consists of elements of the form $a + b\varepsilon$, where $a, b \in \mathbb{R}$. \problem{} Compute $(a + b\varepsilon) \times (c + d\varepsilon)$. @@ -33,11 +32,7 @@ Compute $(a + b\varepsilon) \times (c + d\varepsilon)$. \definition{} Let $f(x)$ be an algebraic function $\mathbb{R} \to \mathbb{R}$. \par -(that is, a function we can write using the operators $+-\times\div$, powers, and roots) \par -\note[Note]{ - Why this condition? These are the only operations we have in an ordered field! \\ - Powers, roots, and division aren't directly available, but are fairly easy to define. -} +(that is, a function we can write using the operators $+-\times\div$ and integer powers) \par \vspace{2mm} diff --git a/Advanced/Nonstandard Analysis/parts/1 extensions.tex b/Advanced/Nonstandard Analysis/parts/extensions.tex similarity index 78% rename from Advanced/Nonstandard Analysis/parts/1 extensions.tex rename to Advanced/Nonstandard Analysis/parts/extensions.tex index b88508f..90c1ecd 100644 --- a/Advanced/Nonstandard Analysis/parts/1 extensions.tex +++ b/Advanced/Nonstandard Analysis/parts/extensions.tex @@ -13,7 +13,7 @@ % If you edit this, please give credit! % Quality handouts take time to make. -\section{Nonarchimedian Extensions} +\section{Extensions of $\mathbb{R}$} \definition{} An \textit{ordered field} consists of a set $S$, the operations $+$ and $\times$, and the relation $<$. \par @@ -49,7 +49,16 @@ An ordered field must satisfy the following properties: \end{itemize} \definition{} -An ordered field that contains $\mathbb{R}$ is called a \textit{nonarchimedian extension} of $\mathbb{R}$. +An ordered field that contains $\mathbb{R}$ is called an \textit{extension} of $\mathbb{R}$. + +\definition{} +The \textit{Archimedian property} states the following: \par +For all positive $x, y$, there exists an $n$ so that $nx \geq y$. + +\theorem{} +All extensions of $\mathbb{R}$ are nonarchemedian. \par +Proving this is difficult. + \vfill \pagebreak @@ -71,7 +80,8 @@ Which of the following are ordered fields? \problem{} -Show that each of the following is true in any ordered field. +Show that each of the following is true in any ordered field. \par +The list of field axioms is provided below, for convenience. \begin{enumerate} \item if $x \neq 0$ then $(x^{-1})^{-1} = x$ \item $0 \times x = 0$ @@ -89,8 +99,36 @@ Show that each of the following is true in any ordered field. % And thus $(x^{-1})^{-1} = x$ %\end{solution} - \vfill + +\begin{itemize} + \item \textbf{Properties of $+$:} + \begin{itemize} + \item Commutativity: $a + b = b + a$ + \item Associativity: $a + (b + c) = (a + b) + c$ + \item Identity: there exists an element $0$ so that $a + 0 = a$ for all $a \in S$ + \item Inverse: for every $a$, there exists a $-a$ so that $a + (-a) = 0$ + \end{itemize} + + \item \textbf{Properties of $\times$:} + \begin{itemize} + \item Commutativity + \item Associativity + \item Identity (which we label $1$) + \item For every $a \neq 0$, there exists an inverse $a^{-1}$ so that $aa^{-1} = 1$ + \item Distributivity: $a(b + c) = ab + ac$ + \end{itemize} + + \item \textbf{Properties of $<$:} + \begin{itemize} + \item Non-reflexive: $x < x$ is always false + \item Transitive: $x < y$ and $y < z$ imply $x < z$ + \item Connected: for all $x, y \in S$, either $x < y$, $x > y$, or $x = y$. + \item If $x < y$ then $x + z < y + z$ + \item If $x < y$ and $z > 0$, then $xz < yz$ + \item $0 < 1$ + \end{itemize} +\end{itemize} \pagebreak diff --git a/Advanced/Nonstandard Analysis/parts/x supremum.tex b/Advanced/Nonstandard Analysis/parts/supremum.tex similarity index 98% rename from Advanced/Nonstandard Analysis/parts/x supremum.tex rename to Advanced/Nonstandard Analysis/parts/supremum.tex index 8078f18..bd0dbf7 100644 --- a/Advanced/Nonstandard Analysis/parts/x supremum.tex +++ b/Advanced/Nonstandard Analysis/parts/supremum.tex @@ -14,7 +14,7 @@ % Quality handouts take time to make. -\section*{Bonus: The supremum \& infimum} +\section*{The supremum \& the infimum} \definition{} In this section, we'll define a \say{real number} as a decimal, infinite or finite.