author paulson Fri, 13 Jul 2001 17:55:35 +0200 changeset 11416 91886738773a parent 11415 34a76158cbb8 child 11417 499435b4084e
indexing
--- a/doc-src/TutorialI/Types/numerics.tex	Fri Jul 13 13:58:41 2001 +0200
+++ b/doc-src/TutorialI/Types/numerics.tex	Fri Jul 13 17:55:35 2001 +0200
@@ -19,10 +19,10 @@
shows the most important operations, together with the priorities of the
infix symbols.

-
+\index{linear arithmetic}%
Many theorems involving numeric types can be proved automatically by
Isabelle's arithmetic decision procedure, the method
-\isa{arith}.  Linear arithmetic comprises addition, subtraction
+\methdx{arith}.  Linear arithmetic comprises addition, subtraction
and multiplication by constant factors; subterms involving other operators
are regarded as variables.  The procedure can be slow, especially if the
subgoal to be proved involves subtraction over type \isa{nat}, which
@@ -39,6 +39,7 @@
\subsection{Numeric Literals}
\label{sec:numerals}

+\index{numeric literals|(}%
Literals are available for the types of natural numbers, integers
and reals and denote integer values of arbitrary size.
They begin
@@ -55,7 +56,7 @@
integer division and remainder.  Fractions of literals (expressed using
division) are reduced to lowest terms.

-\begin{warn}
The arithmetic operators are
overloaded, so you must be careful to ensure that each numeric
expression refers to a specific type, if necessary by inserting
@@ -75,8 +76,10 @@
\end{warn}

\begin{warn}
-Numeric literals are not constructors and therefore must not be used in
-patterns.  For example, this declaration is rejected:
+\index{recdef@\protect\isacommand{recdef} (command)!and numeric literals}
+Numeric literals are not constructors and therefore
+must not be used in patterns.  For example, this declaration is
+rejected:
\begin{isabelle}
\isacommand{recdef}\ h\ "\isacharbraceleft \isacharbraceright "\isanewline
"h\ \#3\ =\ \#2"\isanewline
@@ -87,21 +90,24 @@
\begin{isabelle}
"h\ i\ =\ (if\ i\ =\ \#3\ then\ \#2\ else\ i)"
\end{isabelle}
+\index{numeric literals|)}
\end{warn}

\subsection{The Type of Natural Numbers, {\tt\slshape nat}}

+\index{natural numbers|(}\index{*nat (type)|(}%
This type requires no introduction: we have been using it from the
beginning.  Hundreds of theorems about the natural numbers are
proved in the theories \isa{Nat}, \isa{NatArith} and \isa{Divides}.  Only
in exceptional circumstances should you resort to induction.

\subsubsection{Literals}
-The notational options for the natural numbers can be confusing. The
-constant \isa{0} is overloaded to serve as the neutral value
-in a variety of additive types. The symbols \isa{1} and \isa{2} are
+\index{numeric literals!for type \protect\isa{nat}}%
+The notational options for the natural numbers are confusing.  The
+constant \cdx{0} is overloaded to serve as the neutral value
+in a variety of additive types. The symbols \sdx{1} and \sdx{2} are
not constants but abbreviations for \isa{Suc 0} and \isa{Suc(Suc 0)},
respectively. The literals \isa{\#0}, \isa{\#1} and \isa{\#2}  are
syntactically different from \isa{0}, \isa{1} and \isa{2}. You  will
@@ -140,14 +146,15 @@
Various distributive laws concerning multiplication are available:
\begin{isabelle}
(m\ +\ n)\ *\ k\ =\ m\ *\ k\ +\ n\ *\ k%
(m\ -\ n)\ *\ k\ =\ m\ *\ k\ -\ n\ *\ k%
-\rulename{diff_mult_distrib}\isanewline
+\rulenamedx{diff_mult_distrib}\isanewline
(m\ mod\ n)\ *\ k\ =\ (m\ *\ k)\ mod\ (n\ *\ k)
-\rulename{mod_mult_distrib}
+\rulenamedx{mod_mult_distrib}
\end{isabelle}

\subsubsection{Division}
+\index{division!for type \protect\isa{nat}}%
The infix operators \isa{div} and \isa{mod} are overloaded.
Isabelle/HOL provides the basic facts about quotient and remainder
on the natural numbers:
@@ -155,7 +162,7 @@
m\ mod\ n\ =\ (if\ m\ <\ n\ then\ m\ else\ (m\ -\ n)\ mod\ n)
\rulename{mod_if}\isanewline
m\ div\ n\ *\ n\ +\ m\ mod\ n\ =\ m%
-\rulename{mod_div_equality}
+\rulenamedx{mod_div_equality}
\end{isabelle}

Many less obvious facts about quotient and remainder are also provided.
@@ -174,7 +181,9 @@
\end{isabelle}

Surprisingly few of these results depend upon the
-divisors' being nonzero.  That is because division by
+divisors' being nonzero.
+\index{division!by zero}%
+That is because division by
zero yields zero:
\begin{isabelle}
a\ div\ 0\ =\ 0
@@ -186,20 +195,21 @@
simplification rules.  In \isa{div_mult_mult1} above, one of
the two divisors (namely~\isa{c}) must still be nonzero.

-The \textbf{divides} relation has the standard definition, which
+The \textbf{divides} relation\index{divides relation}
+has the standard definition, which
is overloaded over all numeric types:
\begin{isabelle}
m\ dvd\ n\ \isasymequiv\ {\isasymexists}k.\ n\ =\ m\ *\ k
-\rulename{dvd_def}
+\rulenamedx{dvd_def}
\end{isabelle}
%
Section~\ref{sec:proving-euclid} discusses proofs involving this
relation.  Here are some of the facts proved about it:
\begin{isabelle}
\isasymlbrakk m\ dvd\ n;\ n\ dvd\ m\isasymrbrakk \ \isasymLongrightarrow \ m\ =\ n%
-\rulename{dvd_anti_sym}\isanewline
+\rulenamedx{dvd_anti_sym}\isanewline
\isasymlbrakk k\ dvd\ m;\ k\ dvd\ n\isasymrbrakk \ \isasymLongrightarrow \ k\ dvd\ (m\ +\ n)
\end{isabelle}

\subsubsection{Simplifier Tricks}
@@ -228,9 +238,9 @@
the two expressions identical:
\begin{isabelle}
m\ +\ n\ +\ k\ =\ m\ +\ (n\ +\ k)
m\ +\ n\ =\ n\ +\ m%
x\ +\ (y\ +\ z)\ =\ y\ +\ (x\
+\ z)
@@ -252,17 +262,20 @@
\begin{isabelle}
\ 1.\ Suc\ (i\ +\ (m\ *\ n\ +\ j\ *\ (k\ *\ l)))\
=\ f\ (i\ +\ (m\ *\ n\ +\ j\ *\ (k\ *\ l)))%
-\end{isabelle}
+\end{isabelle}%
+\index{natural numbers|)}\index{*nat (type)|)}
+

\subsection{The Type of Integers, {\tt\slshape int}}

+\index{integers|(}\index{*int (type)|(}%
Reasoning methods resemble those for the natural numbers, but induction and
the constant \isa{Suc} are not available.  HOL provides many lemmas
for proving inequalities involving integer multiplication and division,
similar to those shown above for type~\isa{nat}.

-The absolute value function \isa{abs} is overloaded for the numeric types.
+The \rmindex{absolute value} function \cdx{abs} is overloaded for the numeric types.
It is defined for the integers; we have for example the obvious law
\begin{isabelle}
\isasymbar x\ *\ y\isasymbar \ =\ \isasymbar x\isasymbar \ *\ \isasymbar y\isasymbar
@@ -290,7 +303,8 @@
prefix~\isa{z} in many theorem names recalls the use of $\mathbb{Z}$ to
denote the set of integers.

-For division and remainder, the treatment of negative divisors follows
+For division and remainder,\index{division!by negative numbers}
+the treatment of negative divisors follows
mathematical practice: the sign of the remainder follows that
of the divisor:
\begin{isabelle}
@@ -334,11 +348,13 @@
\isa{c} to be zero.  However, \isa{c} cannot be negative: a counterexample
is
$\isa{a} = 7$, $\isa{b} = 2$ and $\isa{c} = -3$, when the left-hand side of
-\isa{zdiv_zmult2_eq} is $-2$ while the right-hand side is~$-1$.
+\isa{zdiv_zmult2_eq} is $-2$ while the right-hand side is~$-1$.%
+\index{integers|)}\index{*int (type)|)}

\subsection{The Type of Real Numbers, {\tt\slshape real}}

+\index{real numbers|(}\index{*real (type)|(}%
The real numbers enjoy two significant properties that the integers lack.
They are
\textbf{dense}: between every two distinct real numbers there lies another.
@@ -400,7 +416,8 @@
\rulename{realpow_abs}
\end{isabelle}

-Numeric literals for type \isa{real} have the same syntax as those for type
+Numeric literals\index{numeric literals!for type \protect\isa{real}}
+for type \isa{real} have the same syntax as those for type
\isa{int} and only express integral values.  Fractions expressed
using the division operator are automatically simplified to lowest terms:
\begin{isabelle}
@@ -417,15 +434,17 @@
Type \isa{real} is only available in the logic HOL-Real, which
is  HOL extended with the rather substantial development of the real
numbers.  Base your theory upon theory
-\isa{Real}, not the usual \isa{Main}.  Launch Isabelle using the command
+\isa{Real}, not the usual \isa{Main}.%
+\index{real numbers|)}\index{*real (type)|)}
+Launch Isabelle using the command
\begin{verbatim}
Isabelle -l HOL-Real
\end{verbatim}
\end{warn}

Also distributed with Isabelle is HOL-Hyperreal,
-whose theory \isa{Hyperreal} defines the type \isa{hypreal} of non-standard
-reals.  These
+whose theory \isa{Hyperreal} defines the type \tydx{hypreal} of
+\rmindex{non-standard reals}.  These
\textbf{hyperreals} include infinitesimals, which represent infinitely
small and infinitely large quantities; they facilitate proofs
about limits, differentiation and integration~\cite{fleuriot-jcm}.  The